A fantasy of mine:
Erin is moaning while another man fucks her. She knows I am naked, masturbating, just on the other side of the door... peeking through a crack in the door frame from the bathroom. Watching him fuck her... her arms are holding onto him... he legs as spread wide with her feet flailing about... she is doing her best to hold onto him while he cums inside of her.
He thinks I am at work... he does not know she is moaning for me. He does not know I am watching him fuck her. He does not know that as soon as he leaves, I will join her in our bed, holding her... cleaning her up... making sure she gets the orgasm he did not take the time to give.