Mine is a minor son, so I don't have the option of not continuing contact at this point. If I did have that option I think I would definitely keep up that boundary, or at least some kind of limited boundary like take him out to dinner on his birthday. The bottom line is he has made my whole family miserable. He offers us nothing but heartache. My only reason to stay connected after 18 is to soothe my conscience and keep tabs on him in order to raise a red flag with authorities if I see him getting out of hand. At some point after 18, I will have to drop my parental concerns of responsibility. However, I do worry about him hurting others and would feel responsible, which I probably should not.
You can do much better than this X. You don't need him, you need to be free from him. Find a real person who can actually hear, empathize, and care and not just pretend they are caring. You don't need those head games.