I think a lot of women here have been cheated on and so they will find all this particularly triggering, and will be projecting some of their feelings onto the situation. I've not been cheated on (as far as I know) but I have some experience of this situation from the side of your friend.
I wondered where the behaviour of my friends husband came from, as like I say it wasn't just towards me. He clearly loves my friend, though, and she clearly loves him. It was just weird what he did, and it wasn't a secret either. Me and my friend discussed it quite a bit, and pulled him up on it directly together a couple of times.
I wondered whether he tried to test her all her female friends to see if we would betray her, or something. Or just to test our mettle, to see if we had 'banter' or insecurities, or other weaknesses. It always felt like some kind of test, but I could never figure out what exactly he was trying to achieve. Sometimes I thought he was trying to isolate her by making her distrustful of all her female friendships. I just felt on guard all the time, though. I imagine your friend might feel the same.
Could you and your friend could speak to your husband about it together, to show a unified front? It just needs to not be anything resembling therapy. Once the problem has been identified, he needs to take that to his own therapist for further support and exploration.
Could you afford for him to go private?