Ok here is my advice:
1.) Tell your friend(the bully) how you feel. Also let her know that you dont want to be friends anymore if she keeps bullying your bestie. (If your ok with that)
2.) Tell him! 90% of the time guys are mean to you because they like you. But it he has hit you or spread rumors about you the dont! Only if its like "playful" mean if you get what im saying.
3.) If you really dont like her anymore, end it. Tell her privatly in a nice way. You dont really think that your friendship is working out but you guys can still say Hi in the halls. You dont have to become enemies.
Hope i helped!
Hi! I'm piper. Comment me if you have any questions. I'm sadly not a junior mod, but I'm working on it