I know it's scary, but if you think about it, how much further away can he get than he already is?
Right now, you're priority is your children. Sweetie, if your H was in his right mind at all, they would be his, too. So, while he's on his ride on the mothership, it's up to you as the sane and responsible parent to make sure your children have their needs met.
I just want you to know your H isn't especially evil, many MLCers do what he's done. It's all part of the spectrum. It just gives you an idea of how truly messed up they can get. If you haven't, read Brooklyn's story. Her XH's antics will make your head spin.
I don't know the laws in your state concerning C/S. Looking it up on the internet in your state may give you some answers of who to contact. If not, you can try calling your local Family Court on Monday. They will be able to help you get started.
I know it's hard, but doing this sooner rather than later is in you and your children's best interest.