My guess is, she's sexually repressed. Brad left her for a chick that's wild in the sack, unless he's a total freak, and she drew the line. Lets face it, she is hot, she doesn't seem like she would be unhygienic. As far as her personality, who knows, we've never lived with her, and she does always seem to have a sort of sour puss look on her face. Maybe she has a little bit of a bitchy side, or maybe she's a control freak. She has gone through a few boyfriends since they split...kinda makes me think it was her.
This is all gossip so who knows what's really true, but based on a lot of what I've read, she seems to be one of these people who throws out the L-word after just a few dates. She supposedly told Bradley Cooper she was in love with him on their second date. A week later he was going out with Renee Zellweger.