First off, he very likely doesn't want a divorce, he more likely wants to separate so he can have an affair safely. It's a classic manouver that spouses try. They want to test waters and want to come and go from their home as they please. They can't do that living there.
I think its likely more than half of the spouses here who are cheating separated first, then followed up with a PA.
Keep collecting INTEL for the moment.
Is OW married? I would guess no.
When he tells you that you are being too controling give him
"We have children in this home and a marriage to protect. I am protecting YOUR family. If you want to HELP me protect OUR family you would put that phone DOWN."
"If you two are just friends you won't mind me having a look at those text messages right?"
How much support do you have friends/family-wise who you can expose this to?
The idea is you want a team of people to put some additional pressure on him to knock off the EA.
My guess is not much if he's willing to move without much hesitation.
