Currently, my contact with 26 YO AS is an occasional lunch (I go to his town and meet him as I do not want him to know where I live). I always start the lunch with, "My offer still holds that I will help in any way I can if you decide to get help for your drug and alcohol problem." He always declines, but I have a piece of paper with a phone number in the car in case he shows interest. Then we go on with a chit-chat lunch. But it is stressful for me. I will say that sometimes I will go for a couple of months before calling him to make the invitation for lunch (because it is stressful for me), and then it sometimes takes several weeks of my weekly phone calls before he contacts me. So we can go months with not talking to each other. And now that he has the latest crisis of having fathered a child, I find myself not wanting to talk to him just now - for my own sanity.
Bottom line is that you will develop what is comfortable for you. That takes time, and it is a trial-and-error kind of thing. There is no one right answer. Think of this as distancing (rather than detaching) if that feels less harsh.