I think a very brief communication that you feel it is best to break off contact is in order.
You just have to do it in a way that indicates your mind is made up, that you do not wish to discuss it further.
As the others here have pointed out, he KNOWS what the problem is.
Maybe you could make it for a definite time period at first--six months or something. That would give you some time and distance to decide whether you want to be open to the possibility of continuing to stay in touch. You may find the relief from the insanity so attractive by then that you will be ready to move on, regardless what he does. Or you might find that he is in recovery and you are willing to wait and see how that works out.
Hugs, it sounds like you're doing great.