This fellow suspects his girlfriend is cheating on him, but he needs solid proof that she's a fucking slut. That's why he has her tied and blindfolded and lets his homie screw her slurping pussy to see her reaction when she finds out who's actually fucking her. She makes it sight like she's overwhelmed and unwilling at first, but then her slutty side takes over and she enjoys sex with a total stranger as well as a filthy cumshot like a real whore.