Confront him!

You jerk out of your stepdad's grip and turn around beneath the warm shower water. The sight of him standing there in the steam with his cock in his hand adds a new layer of shock. Even in the relative darkness of the shower you can see his eyes fly open with recognition. It's his turn to recoil in shock as he understands at the stunning young blond standing before him, whose pussy he just had his tongue inside, is none other than his wife's daughter.

Despite all the ickyness of the situation, your anger is mostly directed at your stepdad's infidelity. Cheating was what ruined your mom's first marriage with your biological dad, now here is your stepdad at a swinger's party licking a teenager's pussy in the shower. So what if it was your pussy?

"What the hell are you doing here?" You ask, your hands on your hips. "You were just going to fuck some random slut at a swinger's party?"

He takes a step away from you, his hands failing to conceal his erection.

"Sweetheart, now listen, your mom is, uh, your mom-"

"Shut up, you asshole," you wag your finger at him, ignoring your nudity. "You told me and mom that you were going to be at a meeting in the city overnight. This whole time you were just planning your trip to a fuckfest in suburbia."

Shock, fear, and anger wash over him in waves. He seems conflicted about how to handle the situation.