I'd guess not assume that because of past experience as outlined in the original post. Acknowledging that the plural of anecdote is not data, I've run into it several other times. Friends who strongly believed that their boyfriends were homosexual, but didn't want to believe it, only to receive specific proof sometime later. That's why I guessed that his wife probably already knew. Apparently some women don't think of it as cheating on them if it's done with another guy.
Just because you live with someone doesn't mean they can't fool you completely.
Again, this is only a guess, but I'd say this guy wasn't too smart. His crime had a very good chance of getting him in some deep trouble. To be bright enough to hide such inclinations would imply that he'd be bright enough not to do something so stupid.
As the definition of sex gets more narrow with each passing year, huh? Good grief.