You know your S best but it might also just be his personality. I have two girls and when I divorced their father, my eldest would always call the parent she wasn't with to say goodnight. My youngest never did. It was like, out of sight, out of mind. You had to call her if you wanted to talk to her, she was just off doing her thing. But the fact that she treated both parents the same told me that's just how she was, especially since my oldest treated both of us the same too (only she did the opposite). Just a thought. Maybe he's not as tortured as you think.
