The motive of this woman is the hope that he will be caught sporting a love bite, and will conclude the degree that this cheater is willing to go to protect this affair with her. She could be madly in love with this guy and is willing to go to any length to keep him, even if it means that the cheater's wife will evict him from the relationship. This would then ensure her the security that he will have no other recourse but to go to her. If the former was not her intent, but rather occasional flings then she would have ensured that no telltale clues surfaced.