Ex-fiancee and I started dating again back in college. She got all religious and righteous on me the first time around, so I broke up with her. About a month or two later, we started dating again. Although we agreed that we were "exclusive", she mindfscked me for the next two months while she started hanging out with old boyfriends, guys who made it obvious as hell that they wanted a piece of her, and basically just any guy who would give her the time of day. I was lucky to see her one day a week. When I asked her to hang out, she always had plans with one of these other guys (there were 4 or 5 in total, including myself). Whenever I called her, she was always on the other line with one of them and told me she'd call me back. She'd call me back right as she was heading out the door so we could only talk for a few minutes.
I don't think she was trying to "get back" at me for breaking up with her, but the first break-up made her distrustful I think, and she wanted to keep her options out there. One night I just blew up over the phone about it (this was after she returned home after taking one of these guys to dinner with her parents). Apparently they all had a nice long conversation about how she should break up with me, so she did.
We both needed to get away from each other, and in the long run, I'm glad it happened, but those two months were absolutely miserable. I really cared for her a lot, even during the first break up. The first break up was just the result of her drastically changing her personality. I was stupid for thinking the second time around would be any better, but I really missed the "old" version of her.
Anyway, about two weeks after the second break up, I ran into my current wife. I also had a great group of friends that got me drunk out on the town enough to keep my mind off things. It all came together.