Should I break up with my girlfriend so she can get back with her ex?

This post is long and rambling so if you're short on time just ignore me please

I've recently started going out with a girl I've known for a while. We were never so close to be friends prior to this, but knew each other fairly well from nights out and the like. I also knew her ex-boyfriend in a similar fashion, although I was actually slightly closer with him.

A few months ago she broke up with him, citing numerous relationship issues, not least the fact that she was suffering from depression and it caused many arguments. I think he tried to help and be understanding, but eventually it put too much strain on the relationship, which in turn made other more minor problems escalate to the point that the only solution was to break up. She initiated the break up, and one of the major reasons was that she just couldn't put him through her problems any more. He didn't want the break up as I think he still loved her, but she could no longer make him suffer her mental issues.

In the intervening months I know that she put a lot of effort into getting better, and I think the time alone really helped her. I spoke to her a lot over that time, and it became apparent that we really both clicked. After a few weeks of talking with her, I plucked up the courage to ask her out. She said yes.

Things have progressed steadily since that point, and she says she loves me. However, it's all happened so quickly. We started dating less than a month and a half after she'd broken up with her ex, progressed to intimacy within days of that and she now says she loves me and it's not even been four months.

The worst problem comes when I consider the times that she had with her ex. She told me before we started our relationship and were just getting to know each other as friends that the main reason for breaking up with her ex was her depression. Every other problem stemmed from that, and when I asked whether she thought she and her ex would still be together if it weren't for the depression, she said they most likely would be.

Thing is, I know they were happy together. Like I said, I saw them many, many times and knew them quite well. I was never in their immediate circle (we were friends of friends, so to speak) but I know they shared a lot. They also went out for a long time (nearly twelve years). They shared everything; they were sweethearts from their mid-teens to their late-twenties, they lived together for most of that, holidayed together; basically, did everything together. I can't compete with that, and I don't believe her strength of feeling for me will ever be as strong as that. They were quite clearly utterly in love.

She talks to me fondly about the nights out she had when she was younger, the holidays she had in America and the Med, the films and plays she went to see; all things she did with her ex. Every thing that defines her was things she did with her ex, and I can't ever compete with that.

So, I suppose, my most basic problem here is that I think she'd be much happier back with him; the best times of her life were spent with him, after all. They were happy together, they did everything together. They broke up because she couldn't make him suffer with her mental issues any longer, and those mental issues had caused flare-ups in the relationship itself. But those mental issues aren't a problem anymore. She went out with me so quickly after she'd broken up that I genuinely wonder if I wasn't just a rebound, and whilst we're very close and she says she loves me I know she'll never share with me what she shared with him.

I know he's still single. I also know that she won't tell him that she's seeing someone else, which makes me wonder if she doesn't want him to know she's "moved on". She says it's because she feels guilty because she initiated the break up and now has found someone else, and it breaks her heart to see him still wounded from the ending of their relationship and not seeing anyone new.

I think she still loves him, even if she doesn't realise it. Or, at least, that she will love him when she gives him the chance. They had everything together, and if it hadn't been for her illness (something she herself decided to break up over, not him) they'd still be happy together. I know the distance bothers her, too; I live in Limerick and she lives in Dublin, and he lives in Dublin, too. It gets to her that she sees me only once a week or fortnight in the flesh, and she could see him every day.

Given that the one problem that broke apart their perfect relationship has now been cured, and that they still love each other, would it be fairer on everyone involved if I broke up with her? I know she won't do it even if she wants to, because she couldn't bring herself to break a second boyfriend's heart - she's too nice. But I can do it, if it needs to be done. I'd rather suffer the pain now than be emotionally crippled two years down the line when she realises she should be with him.

Thanks for reading.