While you are still in contact with WS or after you send out a protection email?
It would be interesting to see how he reacts to you sending him an email AND to OW at the same time.. the same letter to both of them.
If he IS thinking you are "moving on".. which I suspect is NOT the case, its just another masked manipulation.. he wants to hear you reassure him that he has you in his pocket...
HIM : You are moving on YOU : I want to save my marriage HIM : I feel better now, I am going to celebrate with OW.. seeya
If he IS thinking you are moving on then he will get a written proof from both you AND OW that this is not the case
( I strongly suspect OW would share this letter with him)
I can't say how he would react.. but I suspect it might jar something...
Let me think on this one.. ask your father too, he's got some background here so he's a good person to poke at, unless he doens't want to hear about him.