I guess your posting is timely for me. I was thinking today about how most of my anger was placed on OW in my case. Who I still think of as a low-life scum of the earth type. (Maybe I am a little biased....) But anyway I have come to realize that my X was acting pretty scummy himself. When I tried to reason with him (Silly Me!) and asked him why it was okay for him to sleep with someone else's wife, my X actually replied: "Well, he is an idiot!" Okay, so that makes it alright.....
But I do think you should not talk to your son about it. Which is hard. I try not to talk to my sons about their dad and as I call her SOW (Sociopath Other Woman). Your son is your son, he will never be her son. When you find yourself wanting to say anything to him about her, picture a big red STOP sign, and STOP! Say to yourself STOP! And change to a nice positive topic.
This may well be one of the hardest things to do. I have complete faith you can do it.
Aloha!
Me 57 XH 58 Sons age 32 & 27 M:32 D final 9/12 Bought 10 Acres and Living the Dream!