Help me!

Okay, I'm not going to say names, so let me start by saying someone I know, has always hated me, bullied me, etc.
so my bff, we've known each other forever. And she (my bff) used to be really good Друзья with that someone I know. So one day, the someone I know thought it would be fun to turn my bff against me. Now I'm really mad because we promised each other we'd never трещина, сплит up. I tried telling my bff the truth. But she never believed me. I thought we would just make up again like we normally do, but now it's been 4 months. How can I get my bff to be Друзья with me again?