Is this girl really my best friend?

So theres this girl i absolutely hate. And i mean HATE. We were once friends and then i relized what an awful girl she is. My bestfriend was close with her too. We all used to hangout together. When we all relized this girl was nothing but drama and a pain, we all moved on and never talked. Maybe a year passed and my bestfriend started to become best friends with her again. They talk about me and they hangout nonstop and they brag about it too. When they talk about me my bestfriend calls me and tells me what they say. It causes me nothing but pain and having hurt feelings. The pitiful ***** is now supposivly trying to talk to my boyfriend everysingle day and her and another one of her friends skype him and tell him hes hot. My bestfriend just recently told me this and didnt speak up for me or anything. Is she truely my friend or is my hatred for this other girl just making me furious at her?