Ts, I am not going to blast you, I agree with you. He needs to man up. It is not ok to do what he is doing to SO.
S, I know you are worried about him not being with the kids. But HE is responsible for his relationship with his children.
My son is much older and I sucked it up in order for h to be able to see his son. I wish I hadnt. It cost me dearly in terms of the damage to my self esteem.
So, I think you should do what TS said. He will have the kids in his life. You will have back yours.
And oh, poor baby, the lightbulb just went off in his head.