So sorry for your difficult times, James.
I wanted to chime in because I am a BW who was cheated on by a NPD spouse of 20 years and there is a good thread on SI, yes. Two counselors have been able to pinpoint the disorder in Perv and one didn't even have to meet him!
It has been a horrible, terrible experience and a word of caution is to tread very carefully, very lightly, as if you are up "against" a bully at school as a kid.
The phrase "pick your battles" has never been more true at this stage in life and I have to decide each and every thing in mine and my children's life now, that has to do with him or about communication with him. I have to present things in a different way than with other people and have had to learn to be covert, where my nature is open-book.
I'm sorry to get so long-winded and could write about it for ages. Once a few things happen as you try to communicate with her, probably you will be able to make patterns out of future communication if you have to have it. If you make demands or put limits or boundaries on WW, it could backfire, but there are ways to do it that are less obvious than a different kind of person.
It's time to think of you more and your son if you can, though I suspect your mind is pretty focused on WW and the A, as mine still does, five months later. The grief periods do abate and other things will slowly begin to matter again.
Your WW sounds lucky, if I may say so, to have your devotion and love and your sons and I'm sorry she's throwing that away. It happened here as well, we were totally 100% devoted to Perv, who turned on us and then abandoned us, never to look back until it suited him and lawyers are looking.
I wish you luck, James and all the best.