The other thing you can give him when he tries to talk now is :
I am not interested in discussing that while you are in contact with that woman.
EVEN M talk... tell him you are open to discussion when he commits to not contacting her...
HE WILL need to hear this from your friend... advising him that she's NOT making reconcilliation any easier... His insistence on maintaining this friendship is quite incriminating to be honest...
If he wanted to reconcile and was not having an affair with her, he would have given her up right away.
He's clearly wanting to get back together... so the only inference we can soundly make is that he's in EA, if not PA... I can't find another explanation as to he wouldn't give her up asap.
He pretty much incriminated himself there with his choices... Right there and then he could have said "Done, she's gone... If that's all it takes..."
He's holding on yet... but you are doing a lot of damage here to his affair... keep it up