1) you don’t have to convince S17. He just needs to know the offer is always there on the table for counseling
2) I’m going to be brutally honest here and I apologize in advance. Boundaries are going to take longer for your H to respect. Because they have been so so weak. He says the right thing, and he’s allowed to come back through the door. You allow him to cuddle with you and talk about OW. You have allowed him to be abusive towards you under the guise of having to treat lightly because he is in his alter ego. He knows he can trounce on you and you will give in with the right words without having to prove much . Your kids as well have seen this. The best way to teach your kids is to model them. And I think you can’t go dramatic on them. He will call BS.
You need to enforce boundaries where he talks about other woman or talks abusingly to you, you immediately remove yourself from the situation. Before letting him anywhere back through that door, you need to consistent long term proof of change. That the monster isn’t coming around anymore and isn’t allowed back.
Best way to teach your kids is to model it. The allow for the counselor to help guide them on having healthy boundaries with their father. Do you have a counselor for yourself to help you with the same ?