Congratulations! I'm so happy things are moving in a positive direction.
Now, be prepared. He will not likely have had his last contact with OW, despite his intentions or sincere commitment to you. I have NEVER seen a clean "final" break with an OW, and I've been coming here since 2002. She will reach out to him wanting closure, or he will find something he meant to give her or remember something he meant to tell her. Blah blah blah. I hope you are the exception, but if not, do not let the death gasps of their R derail you.
This does NOT mean you should be blind to it or accept it. Be clear that it is not OK, be firm with your boundaries, explicit about consequences. Get the zero-contact letter that you get to read and mail, or be on the phone to listen in on the final very specific zero-contact instructions to OW. Require transparency -- free access to phone, email, etc...
And above all, be compassionate. Realize that it will seem cruel to him to ignore her plea for closure. It will hurt not to forward a news story that will interest her. It is not OK, but we aren't perfect. Tell him you know he's a good man. You understand that people do things out of pain that might undermine them. But you also know he is a strong man who is growing. He will do better.
Give him space and time to become the good man that you want. He did not get to a place in his head overnight where the R with OW was OK. It will take him awhile to get far away enough from that place that it seems crazy to him that he was ever there. But he can and likely will, IF you give him the time and space to do it, while respecting yourself.
