How to tell a bad friend you don't wanna be friends with them anymore?

Okay, so my friend who i hav known the longest in my group talks behind my back flirts with a guy i love when shes supposed to be asking him if he likes me & is having a birthday party with all the friends that i showed her & hits me constantly because i get "annoying" when i have ADHD even through its okay when she screams in my ear HI SAMI WHERES YOUR BOYFRIEND JASON? & she says i ditch her when she walks away while im talking to go flirt with guys even though she has a boyfriend... How do i tell her i don't wanna be friends anymore?