Why did treat me like a loser break my heart and then come by leading me on again?

This didn't really make much sense. But I'll try to sort it out for your sake ha. Maybe you initially misread the girl trying to get to know you, despite her boyfriend. Maybe she wanted you as a friend. When you in turn, turn her down, you can't expect for her to want to talk to you. She's embarrassed, hurt, sad, and probably a little angry with you. Not to mention confused. So you trying so hard was too little too late it seems like. At this point, I'd let it go. But its up to you! Good luck :]