Hee hee, the OM had W forward me a text one time. I'm dead serious - forward me a text. I was like, man, is this 9th grade? What a loser wuss.
I responded that one time - but have completely ignored him otherwise. Actually, acted like he didn't exist. If I had got all hot-to-trot, it absolutely would've pushed W right to him.
The only time confrontation works, in my opinion, is when the OM/OW is married, and you out them to their spouse, or threaten to do so - but I'm no professional...