Pissed and confused

So here's the story. My boyfriend has this friend I hate and won't stop talking to her though I've asked many times. I don't care that he talks to girls but this particular girl has tried breaking us up in the past because she thinks I'm not good enough for him. In the beginning she lied about having sex with him then later denied saying it. After awhile she started saying that she didn't have prove anything to anyone. It still pisses me off that he talks to her even though she tried breaking us up. Its like he's choosing her over me. He says he's known her longer than me but that shouldn't matter. We're dating and in love for almost 5 years now. Shouldn't that matter more than just a friend he's known longer who tried breaking him up with the woman he loves? What's your opinions?