Another lurker, read most of the thread...
That he is planting seeds to reunite with you, FG, just takes my breath away.
He apparently is investing quite a bit of his reality in the MYTH that he has created in who you really are. It just doesn't add up that the same person (he beliving this of you-the myth) to have an affair/destroy the family would just out of the blue turn around and want to diminish and down grade what happened to be something so superficial that reflexive off-the-cuff dismissiveness will solve it.
This is total projection. This is what HE has done, and is doing, and he wants to assign you the role of this player in this story. He is the bad guy in this, not you. Don't absorb any of it. You have an invisible shield of Teflon -all of that crap will slide right off of you and down to the sewer where it belongs.
My line for you to your jerk would be:
"I've had enough of your manipulative, duplicitous crap; time for you to move on and tell it to the next one."
I like BalloonSlayers ideas too.
Why would you take him back? That is simple: so he can do it to you again.
I know it is not a black and white world, and even in these circumstances there may be compelling reasons to consider a reunion. However, the betrayal is so deep and clear, that your relationship could never be what it may have been in the past.
That letter dropping through your mail slot may turn out to be a blessing to you and your dc-it has revealed who your husband really is and has given you a prime justification and motivation to be rid of him. Still can't get over the surprise and sudden revelation of it all. Again, cudos to you for responding (and in the moment) as any sane woman would: dump the bastard.
I hope you can move forward as though he does not exist. That is how he has been treating you. Do not listen to his scripted drama anymore: it is like the phone bill record of numbers-you don't need to know it, you don't need to hear it.
Your dc will be fine, or actually better off without an ever present demonstrator of lies and deceit nurturing them.
Take care, thinking of you.