I know that I would be madder than an old wet hen if my "H" was doing this. How does he think his children can ever begin to heal if he's taking them over there? This man is so out of touch w/reality he doesn't even begin to see the damage that he and that ow are doing to his children. Give me that 2x4! I want to smack him over the head and knock some sense into him.
This is unacceptable behavior and now is a very good time to implement some boundaries about visitation, at least until you are divorced.
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.