We heard the phase, what done in the dark? Eventually comes to light. Sounds good and in some cases stands true.
Except for some lovers, mistresses just doesn't care about exposure. Especially if others are aware. Interest attracts, if offered somewhere, you find a willing participant.
Sometimes, affairs go on for decades without being exposed until at a funeral. When children's are mention and from nowhere others start claiming that parent.
Mistresses being around since scriptures. Affairs too. So as much sermonizing that we face in the church hasn't changed habits.