Why does my boyfriend defend his female friend who insulted me?

My boyfriend has a female friend from high school I cannot stand with all my might! I tried to be cool but she once in a drunken state told me that I wasn't good enough to keep my boyfriend. He's 28 and has been friends with her since they were in high school. You can rule him being in love with her out since apparently she dated one of his buddies who he would not break bro code for PLUS another friend of his has been in love with her since school as well. She's a queen bee type who thinks all the guys in the group want to bang her even if she isn't interested in them. Perhaps I was a threat. What I don't get is why every time my boyfriend and I have fought bad it was because I told him how much I can't stand her! Why is he so faithful to a friend who insults his own girl? Should I move on? We've been together for 3 years. I really am looking for guys to please explain this to me
Why does my boyfriend defend his female friend who insulted me?
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