My adult son went through that experience, too. All his kids could talk about was OM. I told him that OM had to win their acceptance. He would buy things, take them places, and give lots of attention to the kids. I told my son that their daddy did not have to win them over, and not to worry b/c it wouldn't last. Sure enough, it didn't. But I saw the raw pain in my child, and it was such a helpless experience as a mom. He felt as if he was being replaced in their lives.
Orange, no man will ever replace you in the heart of your son. It's just natural for a kid to talk about something new, but it will wear off. Try not to let it eat you up, and let's pray the OM is good to him whenever he's around your child.
((hugs))
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!