I would say he has it pretty good where he's staying and the only needs he is not having met by living with his mother & sister...would be his sexual needs. Of course, he should miss his children....and you, but as long as he gets everything he had at home while M, then he will be doing great. I think when he begins to want to satisfy his sexual needs, he will either start dating or else he will warm up toward you. So, be prepared for either way.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
