Just a dumb question here. How can you prove, beyond your own speculation, that someone is having an affair? Don't you have to be in the motel room with them to see them actually having sex? I can't imagine but that I'd be extremely reluctant to report that someone was having an affair, because all I could say is that "it looked like it", not that it is a fact. And you could be made a fool of.
For that matter, my wife and I are not having sex, and nobody seems to have picked up on that. So I don't know how you'd know if somebody was having sex or not.
