The 9th step is to make amends to others unless it would do harm. If it would harm you, you're under no obligation to message him back. If he needs to do it for himself, he can write you a letter that he never sends. If it's that important for him to get a response, then he's baiting a trap to get you to talk to him. Only time will tell. You get to choose when you message him back, and the boundaries are for you. If he gets well, he can do it on his own. After all, he was able to drink on his own, right?