Eventually when he is panicking and your friend gives him the terms :
NO CONTACT with OW
He will try "we're just friends"... the simple retort to this is
"OK, if she's just a friend then NOT CONTACTING her shoudln't be a problem... YOUR WIFE is your FIRST PRIORITY RIGHT?"
My concern at this point is that your H may try to reconcile while still denying an affair... Puppy may comment here but I honeslty don't find that a constructive first step... we need to get your husband to face his fears and his shame and FULLY DISCLOSE what he's been doing with her for n weeks.
I think he's way too embarassed to do that... he's gonna be a tough nut to crack on that end, but in my opinion its a necessary step.
Just focus on No Contact For now.. he may come clean and surprise us all... I am afraid we may need a love letter or something to force his hand...