I think you have to leave the universe of normal. People in MLC (and narcissists and PAs) have no empathy. He is not going to think about you and S. The "empathy" for the OW is nothing more than love bombing. It isn't real.
Next time, you go out and buy the toothbrush and stop waiting for him to do it or take notice. You cannot have expectations of this man. If he does something nice or thoughtful, thank him for it (even if it is something a decent person would have done).
