God knows what's going through his mind. If he now believes that the relationship is over, he may be thinking that it's better if he keeps custody of the children, so that he can dump them on his mother and doesn't have to pay maintenance (and can continue to be a complete miser). So he may take them with him abroad or to his parents' home or God knows what.
Really, this is the most dangerous time. Please, please get yourself and your children away from him.