What should I do?

[miss_understood]

I've been seeing this guy for over a year now, and I really love him. He says he loves me and up until now I have believed him, but I don't know what to do. We're not "dating".
So, when I met him, he was seeing someone else.His girlfriend was visiting family for the summer and it was mid July when we met. Originally, we intended to just be friends. However, we fell for each other and fell hard. We acknowledged this to each other and fought to remain friends, but one thing led to another and we began having a pseudo relationship. This was the first time I'd ever been with a man in a relationship with someone else, but not his first time cheating. Don't get me wrong, he felt really bad about cheating and we decided to stop, and we did. When his girlfriend came back to town, we remained friends but avoided all contact. This was a really hard time for me, but I was dealing with it. Around this time, he started his student teaching (the final step before getting his degree) and he had to move about 70 miles away. Then, his girlfriend broke up with him. He was hurt about it and we waited a while but eventually started sleeping together again. I would drive out to his place at night and get up really early in the morning to make it back for class (college classes for the same degree program he was involved in...that's how we met). About halfway through his student teaching (12 weeks) we both had to attend a conference. We had a huge fight while we were there and met up at around 1am to talk things out. Then, he tells me he's been seeing this other woman, but not really seeing her. They weren't dating (neither were we) but they'd kissed and she didn't know about me. He was really confused and i reassured him. I told myself that he wasn't my boyfriend and we'd never agreed to make anything official or explicit. After the convention, things kinda got bad. I wouldn't see him very often and he'd say when he got back from student teaching we'd see each other more often. When he got back, however, it went from bad to worse. He wouldn't answer my texts and I saw him maybe twice a month. I decided I was fed up with it and slept with someone else (not just some random guy, an ex). He 'forgave' me and I actually started seeing him more often. When summer came again, I saw him every day because the other girl was in Italy. He said he loved me and wanted to leave her but didn't want to hurt her and didn't want to do it over the phone while she was in Italy. Now she's back and he says he doesn't love her and wants to leave her and be with me but they had to work together in a very close environment for a week and he didn't want it to be awkward. I really love him and he seems to really love me and I told him that he had to make a choice or he'd lose me, which he really doesn't want to do. He says he just doesn't want to hurt her and doesn't like her in that way anymore. The work thing ended yesterday and she "made" him go to a concert with her last night about 80 miles away. I guess they ended up staying the night instead of driving back in the dark... I can't close my eyes without seeing him with her and it kills me. I don't want to lose him. I love him more than anything, but this is going to break me. What do I do? He feels like shit for doing this to me and 'plans' on breaking things off with her, but its hurting me. He claims to love me more than anything, including her, and yet he is hurting me to avoid hurting her, and he knows it. I know this all sounds a little teeny, but I'm honestly stuck here. I can't bear the thought of loosing this man.

[MaidenMinx]

You can not lose what you never had.