I sent him a brief email explaining that I no longer wished to be in contact with him until such a time as he had embraced sobriety and had been working a 12-step programme for at least a year. It took me months to even get to that point so I guess I had to be very clear in my own mind as to why "no contact" was in my interest.
Be prepared for fall-out but don't doubt for a minute that you have made a mistake. "No contact" is for YOU and you alone. XABF retaliated with some horrible threats and nasty accusations but I survived thanks to this forum, re-reading chapters of Melody Beattie's books, the help of real life friends and professionals who understood and one memorable conversation with a women's crisis line.
Your A won't let you go easily. You'll probably have to block emails, use caller ID and possibly change phone numbers. Your A will find "hooks" to reel you back so post here and we will help you recognize them.
All the best!
ARL