It's not always guys, girls too.
Why do you keep going on about your ex? If you were talking to your friend, sure. But if it were someone you like/are with, wouldn't it give them the wrong idea?
So why do people do this?
Most Helpful Guy
The short of it is this. They have some baggage left over from the previous relationship. It either means they have feelings for their ex, or there's some resentment, or maybe something about the past still bothers them. Maybe they have trust issues or something. Who knows. Whatever the case it means that they have baggage. This is most likely to occur when someone is on the rebound.
The rebound is that indefinite period of time between when someone just broke up, and when that same someone finally gets over the ex. In that period of time, dating is going to suck for whoever dates them. Because this person will either talk about the ex, or bitch, or maybe even who they're presently dating like they're the ex, or expects they're gonna do something like them. Either way, a rebound is NOT the time to date someone. Thing is you never entirely know when they're in rebound mode or not. It sucks.
Anyway I hope this gave you some degree of insight or enlightenment on this.