How to get over the past

My girlfriend and I have been dating on-and-off for about 2 years. During this time, we've had some extremely rocky situations. We've recently been apart for about 5 months and have just recently started talking again and giving it another try.

Something has effected her mentally, and neither of us are sure if it's depression, bi-polar, anxiety, ect. She's seen a psychologist, psychiatrist, and has tried medication. It usually seems that when she's not in a relationship, she's fine, but when she gets in a relationship, she can't trust anyone and that causes HUGE problems with us.

We've both done a lot of stuff and said a lot of things to hurt each other in the past. But I'm past all of that now. I realize that she's the person I want to be with and I've thought about her every day for the past 5 months.

She keeps bringing things up in the past that hurt her, but I try to change the subject because I want to leave those things in the past. I also know that if we were to start talking about those things, she will start blaiming everything on me, and I DON'T want to start saying things like, "well you said this, and you did this..." She says she can't trust me and can't forget about all of those things. And to a point I understand, but I want to focus on what's happening NOW.

Another thing that makes our relationship and communication difficult is that we live about 2 hours away from each other. Plus, I have a daughter who comes to stay with me every other weekend. So when we're together I usually go visit her when I don't have my daughter, and then she comes to visit me. But with sports coming up, my daughter will have games every weekend and I hope she doesn't get mad that I need to go to my daughter's games. I'm affraid that she's going to think I'm putting my daughter first, which I am. Is that wrong?

The distance keeps us from enjoying a lot of simple things like going to see a movie after work, or just getting to see each other more and developing friendships together. We've talked about living together, which is a big step for both of us, and I feel that we would both really enjoy that. But that adds the stress of her quitting her job and relocating... and she doesn't deal well with stress and anxiety.

Can anyone help with how I can deal with her feelings of the past or how I can reassure her that she can trust me?