Anxiety, Depression, Bulimia and the struggle for love

Hi Everybody,
I'm new to this forum. I want to make it clear that my questions and story is in reference to my (now) Ex girlfriend. I wanted to share what happened between us and perhaps get some insight on what happened. I hope you guys can give me a little clarity.
My ex and I were dating for two years. I have been dumped by her twice now. She is 22, I am 28. When I first met her she had attempted suicide and was in an incredibly dark place for quite some time. Before me she had dated a girl for over a year and done the usual random college hookup thing ( with men ). It is also important to note that she does NOT have any close friends and I never saw her hang out with friends our entire two years together . I was her first serious boyfriend. As time went on, her and I just got a long very well. I saw her pain and darker outlook and I developed that hero mentality. Throughout the relationship there were plenty of great times ( travel, love, laughter, sillyness, intimacy) but plenty of times where she was distant, cold, snappy and somewhat sad. However even though there were tougher times for her, we certainly loved each other immensely. We had just gotten back from a wonderful trip to Arizona with my family, when I unfortunately found out that she had cheated on me with a co-worker. She got drunk and slept with him. As you can imagine, I was devastated. After telling me she was rather cold and distant. She later went back north with her family and completely abandoned me in my pain. About 3 weeks later I decided to send her a note, explaining my stance and my ability to forgive. And while I still had trouble with the idea of her cheating, I knew people make mistakes, especially someone with the issues she has. She returned an email to me explaining how terrible of a person she was and how I should never forgive her. I honestly thought it was over until one day she showed up at my doorstep and we tried again. I learned to trust her again and I feel like our love was incredibly strong. She would constantly text me with loving messages and we saw eachother 4 to 5 days a week. She would talk about commitment, marriage, moving in and traveling together. We had just taken a trip to Europe together and had a trip planned for a few weeks from now. Two weeks ago now, I woke up ( she spent the night and I left for work in the morning) to a note saying she can no longer be with me as I was her first boyfriend , that she wanted nothing more than for me to be the one and that her mental state has become increasingly worse. It is important to note that when we got back from europe she began suffering from Bullumia. She would regularly say she hated herself and the way she looked. She would always say I deserved someone better. She told me multiple times that she struggled extremely hard with boredom ( she has a job only on weekends) and post europe trip and college she was EXTREMELY bored. Thus, she was struggling with Bullumia, taking new depression medication, riddled with anxiety of the future, had no friends, seeing her therapist, and was mentally unstable. As you can imagine, I was blindsided AGAIN by someone I thought i was going to spend my life with. We met up about a week ago and she told me she was moving back north with her family to get better and to start school again. I can't help but feel like I screwed up somewhere in here, but I was nothing but a good boyfriend to her. Why make promises about marriage, moving in and telling me you love me everyday only to dump me and move back home? I know she loves me, that was never in question. I'm just confused as to what kind of mental state she is in now and what I can do from here? I don't think me contacting her is fair, but I'm having a hard time with the idea of moving on from someone I care for so much. If you guys have any insight on this matter or any questions for me please ask.