You are doing great! I am totally supportive of what you are doing, the nice times, the sex. Why not? How are you going to win if you don't compete?
As for your son's behavior....great! Your husband needs to see what it does to the kids and how strongly they feel about their family. This is the stuff that turned my husband around. Yes, we had broken doors and holes in the walls from my son. But his Dad knew that our family mattered. And he needed to get with the program.
It's not good that he two-times you with her. He gets his ego stroked that 2 women want him. i hope he will listen to his son and grow up and be a man. Don't stop what you are doing.