Best friend is a total bitch

I hate my best friend. She always talks about how skinny she is because she knows I'm bigger. She always lies about her weight too. I'm legit 10 pounds heavier than her ACTUAL weight. She says she's 90 flat. She's rude to me because she thinks she's cooler and prettier. Always bashes my style and the way I say things. She uses me because nobody else likes her. My family hates her and always talks crap about her. Idk what to do but she always finds a way back to me. HELP PLEASE