They usually say to let it die off on its own, that you getting involved will make it worse. I would think of contacting him as a Plan B, something to do when you are ready for your W to pack up, leave, and file for divorce.
The fact that he realizes this can happen from personal experience tells me that he isn't too concerned about it, since he is doing it again.
Trust me, from my own situation, your best bet would be for your W to end it. OW ended it in my situation and H is actively calling her, trying to get her to answer the phone.
This is JUST my opinion though, I am no expert. I am sorry you are in so much pain.
