Well I have this "friend" who annoys me?

I have a friend I have been friends with since 6th grade we are freshmen now. She was cool then but she never grew up. Like shes super immature and annoying. Sometimes she is cool but I cannot spend more then five minutes with her without being tempted to punch her in the face. She would chew food then stick her tongue in my face or laugh over stupid stuff. Worst of all she lies ALL THE TIME within my time being friends with her everyone died her grandma died 7 times (she still has one of two alive) and her best friends died, in other words her hamster died. She gets mad if I hang out with anyone else and thinks I'm talking about her because all of my other friends don't like her. I want to have to hang out with her less and I end up saying I already have plans but I feel bad cause I am like her only friend. I also feel bad because her mom is always telling her how fat she is (110 pounds) and she has to lie to her mom about making out with guys and stuff to make her mom proud. She was anorexic for a while because of her mom. Like how can I slowly back away without like being rude. At the same time she always complains about EVERYTHING like her room is two small, she has two houses one up against the boardwalk and another HUGE one for four people. Sometimes I feel like saying "I live in a two bedroom apartment with 6 people so shut up!" I never do though. She hears someone say they don't like her hair she has a meltdown and cries I am just like "dude it's one person who cares, at least nobody's saying crap like your pregnant and stuff" . I know this is confusing but what should I do? Should I just deal with her cause she cant pick out her own clothes (her mom goes to holster and asks them what their most popular sellers are and buys them cause she thinks it will make her popular). Or should I just be like I'm fed up buh-bye?