Sometimes it happens that two perfectly fine people just don't get along. There doesn't have to be anything wrong with either one of them, necessarily. They just don't "click". If this is the case, the only thing to do, really, accept the situation and minimize the discomfort.
Your gut instinct is telling you something about the situation that you should be paying attention to.
Only you can know which one is the case here. I suggest you spend some time considering thes possibilities.
Next, I'd like to look at one thing you said.
Originally Posted by faraday
When my girlfriend shares cute stories about her, I get angry for no reason.
Anger is a covering emotion. Under the anger is always either hurt, fear, frustration, or some combination of these. Examining your anger around this situation may give you some clues to unraveling all these issues, or at least give you a place to start.
There's my $0.02, for what it's worth. Good luck to you.