What should I do if I have this friend/enemy tht I don't wanna be friends with anymore?

so there's this girl in my school who is nice to me sometimes and mean to me sometimes.she's always mean to me when she gets competitive or when I hang around with my other friend.she gets real jealous and tries to make me jealous when I actually don't care.she always tries to compare grades with me jus to see who's better but I don't want to b friends anymore and I'm way to scared to tell her cuz I told her who I like and I'm afraid she'll go tel everyone :(