I was 17, and I was engaged to my high school sweetheart. (Yes, I know we were too young. But we were in looooove...) One day, he gave me the "it's not you, it's me" talk and said that it was nothing personal, but that he just didn't want to be in a relationship. It turns out that he had been cheating on me with my best friend for about a month (I found this out through mutual friends), and a week after the breakup, they started openly dating. Now they're married with 3 kids.
That happened to me, too. Except for the "with my best friend" part -- that's about the only thing that could have made the situation worse. But otherwise, right down to the "they're married with 3 kids now," the exact same thing. I feel your childhood pain. I found living well was the best revenge.

I have dated a few of those and let me tell you they are no picnic. But if I know the type (and I know the type) they will be pleased to have something to help gain them some attention. Even though they will tell you differently, breaking up with them will be a good thing. They can then ride the "pity wagon" until the middle of January, which will make an excellent Christmas gift. Of course his friends will want to pull your hair for throwing fuel on his "needy" fire.
You filthy beast! I like that. 

He realized how dumb a reason that was and we got back together a week later.