I hate this friend so much, so why do i still hang out with her?

well to shorten it down the easiest way to describe her is: bitchy, gets angry about EVERYTHING, controlling and selfish. most people hate her and i dont know why but iv stuck around. she treats me like something on the bottom of her shoe, always talking down to me and belittling me. she makes me feel bad about myself. i have many other friends so its not like im clinging to her because iv got no one else. im just sick of her she demands things from me and yells at me infront of people and its embaressing. iv always been there for her through her hard times and have been nothng but a good friend. but the other day she told me i was being a ***** and needed to sort my **** out. when i asked her why it was apparantly because i got angry that she turned my favourite programme off the other day?? like wtf she walked into my house and turned my tv off of course id get angry. many people think shes insecure because shes like fat as probably classed as morbidly obesse and not good looking. everything has to go her way or she gets angry and is CONSTANLY complaining about how bad her life is when she actually has it really good. like all she does is complain and apparantly her life is bad at the moment because she has to do an assignment like everyone else in my class does. shes also controlling and is trying to turn me away from my friends. what do i do ?:/ im in a bad position to just stop being her friend because im in her course and have to see her everyday.