HI, man, you and I don't seem to get along, but I feel your pain here. Fuck, I've had rediculous relationship problems.
Bodhisattva is very insightful here, because I was going to say the same thing. She has a man coming back in the fall. That's why she asked you if you had a girl coming back. I've been there before with a summer fling, however at least she owned up and admited to it just before her fiance got back for fall classes. Just from what you told us, she dropped you several clues. Sorry you got your emotions fucked with by a selfish bitch. Like I said, I've got alot of experience at that, and know how you feel. Move on bro. She isn't worth it. She's just a player.