imLIN said it all. Definitely wait that 48hrs before sending anything, or even making a phone call.
I think the best thing now is to go dark, avoid him at all costs, get the legal stuff re OW done, and sign nothing. As imLIN says, deflect to lawyer. You have 3 months to go until you get benefits you deserve and preserve in the chance that he might come back. Don't allow OW to profit from this. Not out of vengeance, but justice. If you had had to wait a year or so, then I would've had a different view. But, what's 3 months ... I doubt the D would go through in that amount of time.
Take care.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim