he will have to take responsibility, but if he fights enough (if he wants to), theres a good chance the court might take his side a little more... i.e. more custody, ect. The court may recognize his (i assume) good behavior vs. her current situation, which sounds not-so-good for new children
My buddy was trying to build an arsenal of things to use when he had a slight falling out w his babysmomma. Everything ended very civil and there was no need however.