My best friend is being mean and rude!!?

My best friend has been really rude. I have known her for 6 years. She has always been a little rude from the beggining but still a really good friend to have around. I thought maybe she would get better but she hasn't. She's always been putting me down and acting like I'm and idiot. She also teases and embaresses me in front of my friends. She also thinks that. I have to be around her every second of the day and have no other friends. One day she was talking to someone after cl so I went ahead and went to the next cl. In the next cl she got really mad and was like "why didn't you wait on me!!!". Really rudely. I told her that she didn't always wait on me and that I thought it was ok. She also always puts me down. Almost everyday she says something rude about my outfit or my hair. She is reall making me lose my self confidence. Also I think she gets a little jealous of me because I'm a all A student. Every time I make a good grade she always says somehing like "well at least I actually studied" or "well it doesn't even matter cause these grade don't even count". Also a few times she would run away with another friend saying "we don't hang out wih nerds!!!!!" Really rudely. She is a really nice person when we are at her house or just me and her. Then she always talks about how she's sooo glad we are friends. Bu around other people it seems like she hates me and tries to make me look stupid!! I've tried giving her some space but she always get mad at me for "leaving her" or "ignoring her"!! She also tells me that I'm stupid on a daily basis or your sooo wierd or whispers to other friends behind my back saying things like "omigosh look at her hair it's so frizzy!!!" I try to act nice and go along with it saying thing like " I know today has been a bad hair day". She also bullies me by hitting me and pushing me around saying "did that hurt"!!! Then trying it harder and harder. I know sometimes people do this just to be fun but she does it a lot and I can tell she is trying to be mean not funny. How do I tell her I don't want to hang out with her anymore. We have been friends for sooo long. I do have other fiends I could hang out with but then she always gets mad!!! Any advice is apreciated!!! Thank you in advance!!!