Unwanted House Share

LegacyUser

Background – My boyfriend and I just moved in together earlier this year. We’ve been getting on great and enjoying our time together and generally enjoying it! However his sister got a college course in the same city as us.
His family home where she lives is a neighbouring town. When she first started the course in September she asked if she could stay with us a few of the nights that week. This of course I had no problem with – it’s his little sister (19) and I do get on with her and wanted her to have somewhere to stay. She informed us a number of times about looking for place to stay and had been arranging something with a friend of hers.

It’s now December and she’s basically moved in...she stays most nights midweek and goes home for the weekends. Constantly informs that she has found somewhere to live and will be gone next week but it never happens. It’s four months now and it’s really trying my patience. She does nothing around the house – never washes her dishes just leaves them on table, never tidies her room, hasn’t bought any food just eats ours and hasn’t contributed even a euro to the house. Plus although it's a two bedroom place it's not really suitable for three people to live there comfortable - its fine for a couple but with another person it feels crowded.

I have tried to bring it up with my boyfriend but it just causes tension between us as he is of the opinion that she is his little sister and can stay as long as she wants..she is spoilt rotten by his whole family – has never had job or anything...Am I wrong to be pissed off or am I being unreasonable? I didn’t agree to this when I moved in with my boyfriend

What can I do ? I don’t wanna lose my boyfriend over this or to be honest the relationship I’ve built with his family over this?

coolcat63

Don't pick up her plates, don't buy any food that you won't eat that night - i.e leave the fridge empty - and ignore her room. If she/her brother says anything just play dumb; you hadn't realised she'd finished her meal/you thought one of them was going to buy milk, butter, etc. Just make sure you eat well outside the house and leave them to cop onto themselves.

Oh, and leave the household bills open on the kitchen/coffee table...

Good luck!

LegacyUser

Hey coolcat63, Thanks for good advise but I have tried this already. My boyfriend tidies up after her and buys the food for the house when I don't! He doesn't tidy her room though but it's supposed to be our spare room and I can't use it for anything! It just drives me crazy cause she'll never learn

Daisy M

You have moved in with your bf so it sounds as if your relationship is serious. If this is the case and you have hopes of spending your life with him then you need have a talk with him. You have been more than generous and your bf needs to see things from your perspective. There are two of you in this relationship and your feelings should be taken into consideration.

Big Bag of Chips

Ask her for rent and see how quick she'll move out!

Seriously, approach her with the line, "because you living here has become a more permanent fixture, I think it's time we sorted out rent and bills and stuff".

If your bf isn't going to ask her to move out then the next best thing is asking her to contribute. It may spur her to sort out something with her friends.

Morag

If she is staying in the Guest room then invite someone over to visit and stay over night.

theg81der

My little sister has stayed several times months at a time and sound similarly messy and annoys me ALOT but she`s my sister, full stop, and if my hubby had any issue he`d be told swiftly where to go and I`d really wonder about what type of person he was. Do you have any younger siblings? I would be glad that they`re safe and under my roof where I can be sure there not getting into trouble, especially when they`re in college.

OS119

theg81der wrote: »

My little sister has stayed several times months at a time and sound similarly messy and annoys me ALOT but she`s my sister, full stop, and if my hubby had any issue he`d be told swiftly where to go and I`d really wonder about what type of person he was. Do you have any younger siblings? I would be glad that they`re safe and under my roof where I can be sure there not getting into trouble, especially when they`re in college.

your husband might wonder whether you wanted to live with him, or whether you wanted to live with your sister, and then draw the appropriate conclusions about how strongly you valued your marriage.

did you take that into consideration when you came up with this 'sure, she's family' idea - or did you not consider that to your husband, she's not family, she's just a free-loader who messes up his home?

if you wish to live with your sister, or indeed open your home to the waifs and strays of society, you are free to do so - as is your husband free to decide to live elsewhere - or did his choices not occur to you?

theg81der

OS119 wrote: »

your husband might wonder whether you wanted to live with him, or whether you wanted to live with your sister, and then draw the appropriate conclusions about how strongly you valued your marriage.

Why would he think I don`t value my marriage, he has no doubt about how much I love living with him?

did you take that into consideration when you came up with this 'sure, she's family' idea - or did you not consider that to your husband, she's not family, she's just a free-loader who messes up his home?

Eh no she`s his family too, as is his mine - thats marriage.

if you wish to live with your sister, or indeed open your home to the waifs and strays of society, my sister is not some waif or stray! you are free to do so - as is your husband free to decide to live elsewhere - or did his choices not occur to you?

So I`m suppose to choose between my hubby or sister? There equal to me I`m not going to weight there importance to me. And again I wouldn`t have married a man that didn`t understand the bond I have with my sisters and he wouldn`t have loved me if I wasn`t that type of person - he loves that about me.

Taltos

theg81der & OS119 - please stop pulling this thread off topic. If you have nothing constructive to add to the OPs query please do not post. If you wish to continue your discussion take it to PM.

Further breaches of our charter will result in warnings/infractions/bans.

Taltos

silly

theg81der wrote: »

OS119 wrote: »

your husband might wonder whether you wanted to live with him, or whether you wanted to live with your sister, and then draw the appropriate conclusions about how strongly you valued your marriage.

Why would he think I don`t value my marriage, he has no doubt about how much I love living with him?

did you take that into consideration when you came up with this 'sure, she's family' idea - or did you not consider that to your husband, she's not family, she's just a free-loader who messes up his home?

Eh no she`s his family too, as is his mine - thats marriage.

if you wish to live with your sister, or indeed open your home to the waifs and strays of society, my sister is not some waif or stray! you are free to do so - as is your husband free to decide to live elsewhere - or did his choices not occur to you?

So I`m suppose to choose between my hubby or sister? There equal to me I`m not going to weight there importance to me. And again I wouldn`t have married a man that didn`t understand the bond I have with my sisters and he wouldn`t have loved me if I wasn`t that type of person - he loves that about me.

If it is your hubby's house too then he surely has a say. If its hurting a relationship, which the op has hinted that it might then something has to be said/done. I doubt the sister will be living on the streets if they don't let her say.
I think even if her boyfriend asked the sister to clean up after herself it might help a bit a least.

Firetrap

I wonder would offering to help her find a new place be helpful or just throw fuel onto the fire? Just a thought

theg81der

silly wrote: »

If it is your hubby's house too then he surely has a say. If its hurting a relationship, which the op has hinted that it might then something has to be said/done. I doubt the sister will be living on the streets if they don't let her say.
I think even if her boyfriend asked the sister to clean up after herself it might help a bit a least.

I didn`t say lack of communication was ok thats a sign of a problem in a relationship. Thread carefully when discussing it with your partner you definetely don`t want to turn it into an ultimatum because I would always defend my sister and undestand her behaviour. Its his job to sort her out thou if theres a problem not yours.

Daisy M

She is 19yrs old and presumably this is her first year away from home so it was nice of the op and her bf to offer support until she found her feet in a new city. But surely she needs to grow up a lot? Is it not time for her to know how to pick up after herself buy her own food and start to look for alternative accomodation. Most college students manage this what should it be any different for her. She will never learn to stand on her own two feet if her family continually treat her like a young teenager and not a woman. I do think families should help each other but there needs to be a line. Its one thing the op and her bf helping out while the girl got on her feet but should this girl or indeed her parents have asked both the op and her bf if they were ok with it going on longer?

There is no need for this girl to behave like a child she doesnt have any physical dysabilities that stop her helping out and cleaning up after herself. She is taking advantage of her brother and the ops good nature by never contributing to the household but expecting that it is her right to stay there have food and heat and be able to come and go as she wishes. Surely no one could believe that this type of behaviour is right.

Op as I already said it is your flat too so you should not feel guilty about wanting it to be kept clean and knowing what your "guests" long term plans are regarding staying. Personally I think it may be an idea to sit down with your bf tell him you will accept his sis staying a few nights a week until the end of college (early may), but she needs to give ye yer space at weekends and college holidays and stay at home. That she needs to contribute a little money and help out in the flat. None of these are unreasonable requests and if your bf cant/wont see your point of view then I would start to worry, because if your opinions dont matter now when it comes to his family then you are in for a bumpy ride down the line if they make any unreasonable requests.

Btw I would help out my sister or any family member as would my husband but I would know where to draw the line and I would know when they were taking advantage and would call a halt. The idea of telling my husband where to go if he had a legitimate problem with one of my family members is alien to me.

Beruthiel

OP
You moved in with your b/f. Not your b/f and his sister.
I would have had no problem with someone staying a few nights, but no way in hell would I put up with 4 months ++.
To expect your partner to put up with that without any discussion is the height of rudeness and a total lack of respect to your feelings on the matter.
It does not bode well that your b/f refuses to talk about it with you.
You should insist on a discussion on it and point out to him how it effecting your relationship.
Honestly, this is your private space and having someone invade it long term is just not on.

barleybooley

Please, I moved out of home when I was 17 for college, this girl is two years older than I was and perfectly capable to stand on her own two feet. What I don't understand is how are his parents allowing it? Maybe it's time to talk to them and cry halt to the situation. You're under no obligation here, OP, to put his messy sister up and she IS taking advantage! Why would she bother looking for somewhere when she's in an environment where she feels at ease? Also, I'm sure you and your bf have sex and I can't imagine a two bedroom house would be too forgiving when it comes to noise so how has this not driven her out?

Anyway, you just need to bite the bullet and say to yourself "before the new year starts, she will have moved out" and just go with it.

Best of luck and I really hope it doesn't drive a wedge between you and your bf; if it does, then ye may have to reassess what's important to you both in a relationship.

Neyite

I think you need to move out, sorry.

They both sound selfish. I am with my partner 7 years and he asked me if his sister could use our spare room before offering. I was happy to let him help her out for a few months and we refused to take a penny off her, though she tried to insist on it. It was just a big-brother thing, we didnt need her contribution and were happy to have her as a guest, she was neat and tidy and I get on well with her so I didnt mind at all.

Same way I would check with him first if it was my family. Even if my mother comes to stay for a night or two I ask him if he is happy with it first. Its courtesy and recognising that it is his home too and he is entitled to be comfortable in it. However, if he downright refused to let any of my family stay I would be wondering about us. I come from a family who help each other out from time to time, and dont think I could live with that.

So he should have asked you first, he also should have agreed the boundaries and stuck to them. Equally, she should clean up after herself, and not be a burden to you.

But, if you decide to stay, I think if you force his hand on it you will be at a huge disadvantage. Much better to be subtle and kill her with kindness.

If he dotes on her like a child, it might be something you can subtly use. If she stays out all night, you should "worry" about her. To him. Then let him do the talking. If he is the type of lad that hates the idea of his sister getting intimate with a randomer, or going out getting hammered then this will get his protective antenna humming, and he might even start acting like a bossy dad to her, for instance trying to give her a bit of a curfew, or checking up on her, which in turn, she wont like, "because she is a grown up", and she might move out to give herself more freedom.

Do some more of the cooking and make sure that you cook foods she is not overly fond of. Try to get her to bring a packed lunch to school. When she moans, you can look at your boyfriend as if to say "I try" in that slightly martyered way mammies do

Give her chores, like you would a child, scold her nicely to wrap up warm, or take a heavy coat, or a scarf when she is going out.

Maybe the more you mammy and daddy her, the more she will get the impeteus to move? Its a long move and may not work, but if it did, it might be more successful for you in the long run as you cant be pointed out as the bad guy in the situation.

curlzy

Hey OP,

I can't imagine my bf insisting on his sister living with us and getting into a huff if I disagreed. I really honestly can't imagine it. Because it's my home and his home and it's important for both of us to be comfortable, I would be quite worried about your future with this man to be honest. Is he always such a bully? Now maybe we have it wrong and it's just coming across that way but it really doesn't sound like he gives a f*ck about what you think or feel. Sorry if I'm wrong but it really does read like that. You should be his number 1 priority, not his sister and he should be your number 1 priority.

If you can't have a adult conversation with him in which your wishes are respected and given priority then you could always go the passive-agressive mind games route, i.e. stop having sex because "you don't feel comfortable with his baby sister in the house" or as someone said baby the crap outta her until she moves herself. BUT to be totally honest with you OP, if you need to resort to those tactics to have a comfortable home with your fella then you should just call it quits with him and move out. I honestly can't imagine myself in your position because I just wouldn't accept that kind of crap from a man, anymore than I'd expect him to accept from me.

Best of luck.

Reesy

Big Bag of Chips wrote: »

Ask her for rent and see how quick she'll move out!

Seriously, approach her with the line, "because you living here has become a more permanent fixture, I think it's time we sorted out rent and bills and stuff".

If your bf isn't going to ask her to move out then the next best thing is asking her to contribute. It may spur her to sort out something with her friends.

My humble opinion: Don't do this! If she says yes, and starts paying rent, she no longer has any obligation to leave - ever - and you will have offered her, effectively, the option of staying.

Another point: Sorry, this might be painful, but is there more you can do to make your man want you in the house alone? It just seems a bit odd. Have a really serious chat with your fella. ask him to fix a hard deadline by when she'll be gone for good, but listen out for anything he brings up about your relationship, and explore that with him. This might be the other side of the deal.

Good luck.

thefeatheredcat

If she's always been "spoilt" and never really had to be self-sufficient then she probably would find the prospect of house hunting and doing basic chores around the house daunting and could be lacking in that area. It's not your job to look after her or clean up after her. It's her responsibility and sadly if she was not taught that at home, then she will continue to assume that role of being mammied until something changes.

Try and gain some insight into the non-materialisation of a house share with friends.... she's 19, I assume it's the first time moving out of home, and she should be excited with the freedom of living in a student house, keeping to her own time, parties, friends over, student life and all it's liberties and responsibilities and all that stuff that also includes learning a few life skills. More than likely her friends have all settled into accommodation, and next shuffle is the post Christmas shuffle new term, maybe offer to give her a hand to find a place if her friends aren't lasting bonds (as it takes time to settle in the first term) or if plans to move have fallen through.

Now on your boyfriend, perhaps her being around makes him feel comfortable in being protective of her. Any sibling would want to give necessary accommodation but he is endangering a situation of this being long term and is already an imposition..... you should be asking him why outside the bonds of siblings and necessity that he is ok with it being more than just a few weeks. Perhaps on his side, you two moving in together isn't the best working thing, or perhaps he appreciates having an extra person around to save things getting stale or too familiar with you or just someone else to talk to and interact with (particularly if he previously was in a house share or living at home). His cleaning up after his sister is probably a compromise to keep you happy while also treading on eggshells with dealing with his sister.

The good thing about her not paying rent and not contributing is that there's no obligation upon you and your boyfriend - she can't hold it over you whatsoever (as in she can't say well I pay x amount of rent, you must help me with x, y, z or cook for me or buy food for me, or give me rights in having parties, or look after me etc), she has no say and no entitlement to be there, she is there as your guest until you both decide together that it is going beyond what was agreed to.

Your boyfriend and you need to have a serious talk in a non-confrontational way, perhaps the way to do it is to raise the issue having concern for his sister and the living with friends in college (or the lack of the materialisation of her plan and the reasons behind it) and discuss with that focus, rather than focusing on the non-contribution and mess. Then sit and talk with her.

I would also add, do you know of what her financial situation is? Is she reliant on the grant or does she have savings/part time work or are her folks supporting her? Perhaps it might be an idea approaching that subject with your boyfriend...he may be there too to keep an eye on her and make sure she's alright, but perhaps if the grant hasn't come through or money is tight at home, it could give reason to the lack of moving and contributing and your boyfriend's soft stance on it.

Realistically the situation can't continue indefinitely so probing into other avenues like these might be fruitful.

ILikeBananas

theg81der wrote: »

My little sister has stayed several times months at a time and sound similarly messy and annoys me ALOT but she`s my sister, full stop, and if my hubby had any issue he`d be told swiftly where to go and I`d really wonder about what type of person he was.

So, you're basically saying that you'd be willing to give your sibling free reign to be disrespectful, purely becasue they are your sibling and if your husband were to have a problem with that then his character is questionable. I don't even know where to begin......

OP, you're going to have to have a talk about this with your boyfriend. If he's going to ignore it and have a massive blind spot over this due to the fact that it's his sister then you'd have to wonder how else this is going to manifest itself in the future. You have to put your foot down on this one. Tell him that you've no problem helping out his family but not when they're taking advantage.

theg81der

Theres a difference between having a problem with her messiness and having a problem with her staying. I`m sorry but at that age I hadn`t a clue how much effort went into organising and running a home and I didn`t respect that because I wasn`t aware and I would understand (not tolerate) why my sisters wouldn`t get it at that age. So no bother with hubby giving her a bollockin for not cleaning etc but if he had a problem with her staying full stop he wouldn`t be the person for ME - I love long staying house guests which I regularly have and he likes.

Your partner, who your living with, should be someone who knows you enough to know you dislike living with other people for period of x. I have a sister close in age who wouldn`t let our other sisters stay - she likes her space, but her partner is similar and of course that is an established boundary. My point OP and her partner seem to have a communication issue or don`t understand each other well enough yet.

Zen65

houseshare wrote: »

I have tried to bring it up with my boyfriend but it just causes tension between us as he is of the opinion that she is his little sister and can stay as long as she wants..she is spoilt rotten by his whole family – has never had job or anything...Am I wrong to be pissed off or am I being unreasonable?

I think it very much depends on how you see your relationship with this boyfriend. If this is (for you) just a medium-term relationship for fun then yes, the presence of his sister is an imposition which will take the fun from the relationship. Insist she leaves, or be prepared to leave (and end the relationship) if she doesn't.

But if the two of you are serious, you should be proud (IMHO) of how he treats her. He is being an adult, a protective big brother and it is a very good sign for how he would treat you and your children together. He is displaying unconditional and selfless love for another person, and a man who can do that for a sister can usually do it in buckets for his own kids.

If you try to make an issue of this then you may drive a wedge between you which will eventually be fatal for your relationship. Your boyfriend seeks harmony and a strong relationship with his siblings, and for you to try to undermine that is likely to evoke a very negative reaction from him.

She's 19. She will want her own space and move out. Give it time.

I've had in-laws live with me for some time (many years ago) and honestly I enjoyed the company. I took comfort that if I was going to be home late there would be somebody in the house to keep my wife company. I was grateful for the sharing of chores.

What can I do ? I don’t wanna lose my boyfriend over this or to be honest the relationship I’ve built with his family over this?

What you can do is gently nudge her to do some of the work in the house. You can do this without raising any fuss whatsoever. Simply say with a playful smile e.g. "It's your turn to wash the dishes tonight, after all you're not a guest anymore you're family".

There's no need for drama about it, and no need to cause tension with your boyfriend. You're not dealing with a situation that requires an ultimatum, it just requires some careful handling. You can use this as an opportunity to show how much you value him and his family. If this is a relationship you'd like to see lasting the long haul, then generosity of spirit is a critical skill for you both to practise.


Be at peace,

Z

Big Bag of Chips

Reesy wrote: »

My humble opinion: Don't do this! If she says yes, and starts paying rent, she no longer has any obligation to leave - ever - and you will have offered her, effectively, the option of staying.
.

I did say...

Big Bag of Chips wrote: »

... approach her with the line, "because you living here has become a more permanent fixture, I think it's time we sorted out rent and bills and stuff".

If your bf isn't going to ask her to move out then the next best thing is asking her to contribute.

I went to college in my home town, so I was 21 when I got a job and moved out.. but I moved to my aunt's house in the city where I got a job! So effectively I didn't really move out.. but I did pay rent/housekeeping whatever you want to call it to my aunt. My washing was still done for me - to an extent (or I brought it home at weekends!). Dinners were cooked for me, I was "minded" by my aunt.. but, as another poster mentioned, the time did come when I naturally wanted my own space and independence from my family.

So it's looking like the brother doesn't really want the sister to move out yet, and on top of the sister living there, the OP's problem seems to be that she's living there free of charge and not contributing anything. That's where asking her to at least contribute comes into it. And while she's contributing, and learning a bit of independence (managing money - being responsible for herself), her confidence in herself will grow to where she wants to eventually move out anyway.

As it stands, she has never had to look after herself... in any way shape or form. So start with asking for rent, and taking turns to cook/clean etc. Teach her the basics she will need to stand on her own two feet, and she will eventually fly the nest.

But keeping her there, "babying" her, and not asking her to ever be responsible for herself will in the long term result in a woman, possibly in her 30s still effectively living at home (or the OP's home!), because she doesn't know anything else.

EDIT: Just to add, I'm sure had I gone to college in a different city, or got a job somewhere there was no family, I would have figured it out and grown up a lot quicker than I did.. but because family were there making it "easy" for me, it probably took me a little longer than some to go out on my own!

Although in saying that, I bought a house at 23, married at 25 and by the time I was 30 had built a house and was mortgage free! So even though I was a late starter, I got good at it fairly quick!

LegacyUser

A few things that the feathered cat touched on also cause me to think that there might be some other issue here that you may be unaware of.
Why doesn't she want to move out? Why doesn't she want to have 100% freedom in her own house and to spend time with friends, and to experience a bit of the "college lifestyle"?
Even previously pampered/slightly spoilt teenagers usually still relish the thought of having that new taste of freedom, and all of the new experiences and fun it involves.
What type of student would prefer to live with their brother and his girlfriend?

I know she has her home comforts there, but I really feel like there is something else at play like maybe financial trouble, inability to find a part time job, no financial support from family, and not being able to afford all 3 -rent and food and bills on such small money maybe?

Has she made any new friends yet? Perhaps she is finding it difficult to settle into college, and to meet new people. Maybe she is feeling very lonely and finding it hard to make new friends. People can sometimes keep this a secret and pretend they are settling in fine because they are afraid to admit that they are finding it all very hard, or that they feel lonely or like something is wrong with them for not fitting in.
You say that she spends most nights midweek at your house, so she is obviously not staying over often with any friends, or spending her nights socialising with new friends.
Has she ever brought any new friends over for even a chat? Have you ever heard her speak of any new friends and more importantly any plans she has made with them for going out?
If she has few or no friends she might feel afraid at the prospect of moving in with strangers. Everyone has to usually do this at some stage anyways, but it might be harder if you have no friends outside the house to help you settle in to a new lifestyle and area.

Your boyfriend seems very loving and protective of her. I think this is natural and a very good thing for siblings to be close, but as her parents are also not in any hurry to insist she gets her own place, it makes me wonder if maybe she had a bad experience of being bullied, or suffering from depression in the past? Her family do seem to be very complacent and actually happy with her living with her brother, instead of encouraging her to stand on her own two feet. Of course that could just be natural parental worry for their child that makes them happy she's staying with family,I'm not sure.

I think if it is the case that she is having huge financial trouble, or it is the case that she has just not settled well into college yet with new friends, that you could try to help out as much as you can.
Talk with your boyfriend and herself to get to the root of the problem (if any), and you could offer her advice about how to meet new friends, about who to speak with for help if she is finding the course very difficult, about what additional financial support she may be eligible for from the college etc.
Sit her down and ask her how she is feeling about college so far. As her family don't seem to be doing it, I suggest you could take the role of a kind wise big sister, and take the opportunity to talk through her fears of moving out. You could give her your own experiences, and talk to her about finding affordable places, budgeting in a household, how to handle any problems she might encounter with housemates, and also tell her your fun experiences such as the freedom and/or parties, having your own space etc.

From the sounds of it she has a lot to learn about living independently, but I personally blame her parents for that(though I'm sure they were well intentioned).
You could be the guidance that she clearly needs.
Obviously you have no obligation to do so. You have every right to be angry about this situation, and would have every right to demand a stop be put to it all immediately.
I also think though, that if you did give her a little guidance in life, that you would be entitled to be proud of yourself because it would be a very kind thing to do, and I think she would always remember and be thankful towards you for doing so.
I'd say give it until after Christmas for her to get herself sorted with your help, (or the end of first year at the VERY latest), and make it sure that this situation will NOT be occurring again for her second year.

Regardless of whatever problems she may or may not be experiencing, it is essential that she does her share whilst living in your home. I like the suggestion of saying that "you're not a guest now but family" so chip in! You could set a rota for cleaning duties, and ask that she maybe cooks dinner some of the nights, or maybe buys some of the food that week- whilst all the time still focusing on helping her finding a new place, or discussing her worries.

She does sound like she has been "mammied" far too much by the family, and is therefore quite lazy. But you haven't mentioned anything about her being rude, abusive or cheeky towards you, so I think she just needs a gentle kick in the backside and someone to speak with to guide her towards having her own independence.

Good luck, and fair play for having kept your patience up to this point! I hope ye can all work and talk together to find a happy outcome for everyone.

qwertytlk

Well to be honest, and a little blunt... If shes a spoied etc as you say then clearly she doesnt want to move out as then she would habe to pay for all the things she is leaving you hanging for. Maybe have a word with her, say to her 'you seem to ne having troublt finding a place etc, iv rented loadds of times, why dont i give u a hand' and see how she responds. Or if she cant find somehwere then tell her its no problms to stay here during the wk and give her a list of money that needs to be contributed. Such as rent. Do the maths and work out what her portion would be for 5 nights or whatever. Then when the esb/gas bill comes tape it to the fridge and work out what her portion would be(obv considerbally less than yours as she only living there part time) and as for food, tell her she can contribute to the house shop or buy her own.
The problem here is you have been pussyfooting around her for too long, 4 months is a long time to let this lie. Also clearly her family have ruined her. She needs to wake up and snap out of this buzz of scrounging she is on. She is only doing it because shes getting away with it. Shes an adult now and needs to realise there are certain responsibilites that@ come with that. So she needs to step up and contribute or else move out.
Talk to your bf, lay down the law
tell him your very fond of HIS sister but cant really afford to keep her. If he cant see this and agree to it or come up with another solution then let him pay for her. Shes not your responsibility. If he is willing to end the relationship over this, whcih i doubt he will be, then he defo is not the guy for u in the first place-but im sure it wont come to that. This kid is taking advantage of your kindness and it needs to stop. NOW.