POV Sex with My Stepsister-in-law in the Bathroom While My Wife Is Not Home

My wife’s sis Lynn is staying home for a few days and I can’t believe how horny and slutty she is! Every single time we are alone she’s trying to get me to fuck her and I’m finding really hard to oppose the urge to drill her pussy. But I don’t wanna ruin my marriage! She’s so fucking hot, but. Will this stay a secret between us?