Well I don't know when you know. But when I knew to just cut ties with my best friend of 11 years is when everyone else around opened my eyes up to how two faced she was. That and the fact she tried on numerous occasions to break up my marriage. I just told her that I did'nt want to be her friend anymore because she caused too many arguments between my husband and I. And that I could no longer trust her. Then I have'nt talked to her since. I stil miss her. But I could'nt go on being friends with such a toxic person. So my advice for you is : You know it's time to let your friend go. Or you would'nt be asking. It's hard but at least you won't worry yourself over your friend all the time. That's gotta be alot on your mind. Good luck!