Maybell, If I were in your shoes, I would stay out of it for now. Your xh is making a lot of bad decisions, but those decisions are the lessons he needs to learn in order to grow up.
I don't know if your xh would appreciate you telling him this stuff. He may look at it as if you are trying to break up his lovely little love nest. If you were to say something to him, he could actually tell the gf that you advised him of the situation, which could make things ugly and uncomfortable for the when the children are over there.
Now, if the situation turns ugly and it starts to affect the children, then I would say something...but for now, sit quietly and allow this mess to unfold.
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.
