This feeling... Can you help?

I woke up feeling really great. Never felt better, but that quickly changed. Nothing really happened, it's just that this girl has been on my mind forever. There are times where I just want to throw all what we have away. It's not like we're 'together' or anything. Well we were but that was a long time ago. Anyways, this happened several times before where I would tell her about it, making her cry, not intentionally of course. Then we would continue talking where we would make up and things are the same again. Well besides the pain. This always has has happened. Neither of us can go through it again. In fact, last time this happened, I promised her I'd leave for good. I can't stand hurting her like that because I love her. I'm not sure what causes these feelings. Maybe because we're trying to force something that's not meant to be? I mean we live very far apart and we're completely different people. Please don't hold me to that, that's just what it seems like as of now. Also it's not like it's all my fault either, even though that's what it always comes down to. I could go on about it but I always make her sound worse then she actually is. Well, thanks for reading all of this. Any advice would be great. I've no clue what to do. I just want this pain to go away.