Your "friend" needs to get off the juice. its not not legal for anybody and should he get caught he is going to need a new job.
Cheating on the wifes not cool but shouldn't be a problem at work unless it gets ugly and spills over to work. Somehow it always does and then you have all those IA people involved in your business cause there is almost always some kind of accusations from either wife or the other chic that causes PD involvement.