Are they doing something wrong or is it ok coz they are not doing the naughty business aka are they cheating?

A male friend is married now wants to see another female friends completely waxed private parts but doesnt want to sleep with that person coz he is married but she has show him her bits and she has given him a helping "hand" (no sex but fore play)and both their partners have no idea as the parnters would leave them and be livid I assume- he tells his misses she is chasing him and she tells her partner there is nothing going on - but the whole town is talking about the two of them and each of there partners are not stupid and prob. know but are not saying anything but keeping the peace I guess. I know if I was in that situation I would leave my perspective partner . Those two got together like this while he was engaged and still together on and off , do I warn my friend she is doing something wrong or let them continue til he or she gets burnt in the *** which may split their parnters from them or will it serve her and him right to get burnt in the ***. Coz we all know whats going on !