Communication Issues

I'm looking for some advice on an issue that's been hounding my 2+ year relationship for the last few months. Like the title says, my OH and I have been having serious communication issues, and today we had a fight because of it. (sorry about the long post in advance)

So, backstory: the last couple of months have been tough for us. I'd been injured and was unable to leave my home for about 8 weeks recovering and she's been saving money for a course she wanted to do. As it stands, she's never been particularly good at telling me what she's thinking/feeling unless she's really, really upset. The last few months have been some of the worst though; she consistently avoids speaking to me in any depth about things she's doing (usual bits and pieces of where she's heading out to, things she'd ask me regularly), at times, she completely avoids the topic and focuses on less significant stuff like joking and banter, which didn't bother me at first. As time went on though, she started acting inconsistently: avoiding time together because she - understandably - needed to save, but secretly planning large (5 hour) trips for weekends at a time in different locations, all of which were expensive and I found out about from other people mentioning them in passing - the people she was going there with (all female friends) who seemed surprised I didn't know. I didn't honestly mind until there were some indirect issues effecting me: her complaints about a lack of money, time together being sacrificed because of these trips, and any attempt by me to point this out being shouted down, even if she asked for my advice.

This week, we were planning on spending a day together, it's a journey for us both but she's in her course now, so we were planning it on a day she was already in, to save her money. Yesterday, I once again heard from a mutual friend that she was heading off on another trip on the same day we were meeting up...something I hadn't been aware of. So I brought up the topic to my OH and she filled me in on some details - it was volunteer work, she'd be leaving early in the day, essentially cutting into our plans. I made her aware that the cost to me was a lot for what boiled down to about an hour for the price of a private coach return ticket - about €20 - and that it didn't seem like a good idea, especially if she could head off earlier so that she wouldn't risk arriving in her destination in the evening/when it was getting dark. We rearranged the day, and I told her that I wasn't thrilled that she kept this from me. Everything seemed settled until today as I was double-checking if the new date suited her, and things got out of control. She asked if I was angry about the plans falling through, I said no, that I was just disappointed but she made a commitment to go, I just wish I could have been told so we could have worked things out sooner.

And that's when things exploded, she started saying she could have changed the plans around, that she didn't have to go as early as she did, that she wanted to see me, that she didn't think talking about it was worth the time. I made it clear that it wasn't the issue, that her not making me aware had been the cause of this, and I had to make the best call I could and that she would have done the same (and has, with no problems from me). She contradicted herself multiple times about why she didn't say anything, accused me of being angry the night before (I wasn't, but I was angry now) and that I was being unreasonable. I simply said that it's not her choice to decide what I do and do not need to know (I've never done that to her) and that this was a growing issue she's been having. Suffice to say, nothing got solved tonight, but as it stands I'm kind of shaken. We've had our fair share of arguements, but nothing as one-sided as this.

With all that information, I'm just wondering how we move forward from here? I don't know how to even attempt to approach this, I'm kind of really rattled by the whole thing, maybe I was in the wrong somehow?