I would absolutely love it if you just cut off the whole relationship with him, were upfront with the children about who ow was, and even tell SO taht you're telling the children.
I think you should not let him in your home anymore. Have only scheduled pick up times etc.
If he's as addicted to you as he says he is, and it sure seems like it. He will freak out and be done with ow in less than 2 weeks. ABsolutely. I mean he freaks out with you jsut saying you thought there was more between you than there was.
Please, don't let this drag on forever. Take out your knife and make a solid cut now. Then let him freak, on his own. Let him get rid of ow, let him grieve, let him face his issues, and then let him start working on the M with you.
You have showed him that even though the past R wasn't what he wanted, you are willing and able to change and improve it. You have proven yourself. He knows this. Now cut him off. Completely, hwile you still have any power, self-respect and respect from him.
Love must be tough! Have you read this? And by the way, I do think my advice is Dbusting, because I want him to face his issues and you to be in a healthy R together someday.