I have had to do this with a sister-in-law, Angelus. One of my very best friends. It's been over a year now with no contact, after having sporadic contact for several years. It was a really sad story, my brother died suddenly of rampant cancer, she got addicted to his oxycontin pills, then tried drinking and most drugs as an alternative to treatment to get off the pills, did a 180 in life, terrible parenting at this point to her three children (one now married and two of whom moved out and lived with me for a year) and still in denial. Been in and out of jail so many times, facing prison next time with two felony convictions already, has had many drugged-out deadbeat boyfriends, kids all left her, just terrible. I don't know if she will ever pull out of this spiral, but I know I had to.
I hear this and that now from the kids, with whom I keep in good contact and who are thriving and doing well. I miss the old her, but this new, whacked out version is total insanity, full of lies, and downright dangerous. I just had to let go and try to put her out of my mind. I wanted SO much to "help" her through her grieving and sad situation, but she is just too arrogant and full of her own "theories" for anyone to reach her. She's had bottom after bottom, but keeps using and betraying everyone's trust. I still pray for her and hope that one day she will find serenity and sobriety. But I had my own demons to deal with in my marriage to an alcoholic and with an addicted child, and just life and work. She was a user of anything and anyone, and I had to stop the madness. I stopped answering when she called last March, and haven't talked with her since. She's in jail right now and will hopefully be out for her middle son's wedding in June (she missed the birth of her first grandchild last summer by being in jail also), but none of us are holding our breath. I will treat her as always, with love and kindness, if I do see her. But I will never be her best friend like I once was. I just can't trust anything she says anymore.