Just reading, I feel for you and your S, he is pretty young to encounter something like that. I understand not being able to forget. That is what made me mad when I found out H was still w/OW in March, he kept crossing lines that, in my mind, I knew should be "deal-breakers" for our M.
You love your wife. That is what makes this so hard. And I am guessing you would rather file now and try to end it before that love is converted into hate, or something close to that. B/C you hate what she is doing and what she has become, hate seeing her the way you see her now versus the way you saw her before...
I don't have any advice, I am in no position for that today. But I feel for you and I know you are hurting as much as you are angry. Just thinking of you.