We never know what goes on behind closed doors, so don't judge the breakdown of his marriage, it seems like his ex is getting along fine. She is kind of out of your life now. Don't alienate your son, if you do, you risk losing him, he will never choose you over his girlfriend. Maybe he is in "lust" and thinks his new g/f is the best thing since sliced bread, maybe she is. I would be quite grateful he has found someone else, better that than being alone. If you don't feel comfortable having her in your home yet, try to have a cosy meet before Christmas and then decide. She is your son's potential partner and could be the mother of your future g/c. Be very, very careful how you tread , how you behave now will determine your future relationship with your son, g/f ( maybe she's great !) and any future grandchildren