I don't know what it is, but every girl I date seems to bring up their ex. I hate the idea of bringing up ex's, especially when talking to an SO. It doesn't even matter if the conversation is totally benign, I just don't like them being referenced at all. I broke up with my last two girlfriends because of that. 

Side note: I don't get how people try and stay friendly or even best friends with their ex's. Anytime a girl says she is still friends with an ex I cross her off because I know I would not be able to trust her. Is this just a BPD thing that it's easy to wipe someone from memory and move on because I hate the thought of thinking of someone who made me mad?