What do i do about her? my best friend?

so my best friend is being really mean to me and idk what to do so a while ago i hookedup with her ex that she brokeup with a long time ago just go read taht whole question i asked abouthit and now shes seriuosly flipping out at me and stuff and like idk what to do im kind of scared she keeps calling me stupid b**** and making fun of me and im like tellingher stop we can still be friends its ok i dont even like your ex but she wont stop ah idk what to do and she is threatening to tell people all the secrets ive ever told her...help!