The Best Friend and the Boyfriend

I'm not as close with my girlfriends as I once was. I used to have best friends and now I sort of just have... old best friends who now have new best friends. It's a long story of mental illness and breakdowns. But, anyway, The one friend I do still consider a best friend... Well, she and my boyfriend fucking hate each other. I have no idea what to do. I don't know what it is with them. They're both stubborn and blunt as hell. Is it a thing for Capricorns and Libras to butt heads? Because, my God.