I think Obi makes sense, but one other thought that goes along with your examples is this. When you buy a shirt, pick out a tutor, etc, you are not really doing something directed at him or who he is. When you talk about behavior, though, you are talking about him. If he is anything like me, he probably hears you saying he is a bad person. That will elicit a negative response.
Just a thought, because I could be dead wrong. Unfortunately, your boundaries are the right ones, so stand your ground (And make sure you have a Louisville Slugger for the times he gets obstinate. Just kidding).