He was going through his sister's bedroom when she wasn't home. I said, do you have permission to be in there?

He loudly said I just wanted him to feel guilty.

When I explained that I thought his sister deserved that respect, he talked over me like it was important to him that he didn't hear me.

When I said I would do the same for any of us, he became hurtful.

So I asked him if this is about me being nice to him, and he reacted strongly with ridicule. He gave the strong suggestion that he has become overdependent on the relationship with his mother to protect him from having to recognise others in his life.