<human>: Can you summarize the given text in a few sentences?

Okay so I used to have this best friend, but we had an argument and we don't talk anymore as i can now see that hes not a good person. Before we started dating, they didn't know each other and they met through me. Also, its worth adding that my girlfriend lives back home and I live away for college. Anyway, they are now hanging out pretty frequently which kind of bothers me as she knows how I feel about him but she doesn't care. I even came home for a weekend a few weeks ago and she told me that he was throwing a party (that i clearly wasn't invited to) and that she was going instead of seeing me on my last day home. It took me getting upset about that until she decided not to go which I think she decided just so I don't get mad at her and not because she would rather see me than go to his party. 
I want to tell her that it's making me really uncomfortable and kind of mad that she keeps hanging out with him but I don't know how to go about asking her to hang out with him without sounding like an asshole. How should I go about doing this?
<bot>: Girlfriend keeps hanging out with guy i really don't like, almost ditched me on one of two days that I can see her for a month to go to his party, how can i tell her its making me uncomfortable?