You are in the middle of a divorce....Why do you care?
It's not as though you are going to be spending the rest of your life with him. It's not unusual for men to try and jump right back into the dating scene or having sex with women soon after a relationship ends or has been decided upon as being over. Sex, Alcohol, Drugs, and Food are tools often used by people to cope with a divorce or breakup. People do whatever makes them feel better or helps them get through with the least amount of pain.
Your focus should be on YOU.
After all your future lies ahead of you and not behind you.
It's time to stop looking backwards.
Best of Luck!