if you associate with him after knowing this, you are a damn fool in my opinion. let the women do their thing and let your wife know exactly what is up. his wife may be up to some sort of schit too. i made up my mind many decades ago to not associate with scumbags. and i know/knew a lot of scumbags of all types. i lost quite a few "friends" over this decision.
and no, i would not narc on him. just get rid of the situation entirely and consider yourself lucky
