golf mom, I'm sorry to read that your h has now moved in w/someone. We can only "assume" that it is the ow. I'm sorry about the way that he dropped this information on your son. It's not easy for your child to have to deal w/this situation and it is a lot to process. If your son opens up and talks to you about it, please listen and and reassure him that his father does love him, no matter what.
Hugs to you and your family. It's never easy dealing w/an mlcer.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
