you should let the guy and his wife be. giving grief to the guy is pointless... his relationship with her is way more important than yours with him... after all she's the one who sleeps with him... not you...
I'm not suggesting that the wife is being reasonable but the ship's sailed for this guy. and at the end of the day, the husband-wife relationship is more important than any other consideration. so, the guy should put with it for the sake of peace in the marriage... and if I was the guy's friend, I wouldn't say anything to the guy...