I think you should connect with Heartbroken, since her stroy is similar: flip-flopping husband who can't be rid of OW.
Calm down.
Here are my thoughts:
If you are done with him:
Be done. Seek legal counsel. Lay out all the issues. Choose a mediator, but retain your lawyer to go over all the agreements.
If you are not done with him:
1. Since he is the one who wants to reconcile. Find a good pro-marriage counselor and go through the book After the Affair by Janis Springer. It has chapters on ending the affair, etc.
2. If he says he's ended the affair, then ask for proof. Phone logs (mobile and land-line) access to all email accounts.
3. Ask him to send a letter to OW saying he's done and have him show it to you.
4. Call OW to aknowledge he's done. )I'm iffy on this, but it you've spoken to her before....go ahead)
