Lust takes over.

A switch goes off in your brain. Riley is rubbing your package through the thin material of your shorts, and her eyes are locked into yours with desire. You can feel the last shreds of decency vaporize in that gaze.
You grab Riley's perfect ass with both hands, and pull her close for a passionate kiss.
"Mmmm...." she moans appreciatively as you explore her mouth with your tongue. You hook your hands under her ass and pull her up into your arms. She wraps her legs around your hips and continues to kiss you with abandon.
"Daddy..." she whispers against your ear. "Please... please make love to me."
"I could never say no to you, baby..." It feels so wrong... but you do love her. Her body is amazing against yours and your cock is screaming to be put inside something warm and tight.
You throw Riley over your shoulder, and she giggles as you carry her up the back deck and set her down by the sliding glass doors.
Inside, you can see Allison. She's passed out on the couch watching Floribama Shore. Perfect.
"Take me to your room, daddy." Riley is holding you from behind, and her hands are down your shorts, rubbing your cock. "Fuck me where you fuck Mom..."
"Riley...that's so fucked up... I love it..."
"I'm a fucked up girl. I need daddy's cock to set me straight."
You open the door and the two of you sneak upstairs to your bedroom. You push the door closed, and Riley flops face down on the bed, removing her bikini top, then swiveling to face you, legs up, tits out, and grinning.

"I wanna suck that big thing."
You drop your shorts and pull your shirt over your head. Your cock springs at attention, and as you walk it over, Riley is hypnotized, as if by a snake.
"Wow..." Riley laughs in disbelief... "It... it felt thick...but seeing it..." She reaches out to stroke the head. "You have the perfect cock, daddy."
You lay down in your normal spot, and Riley crawls between your legs, stroking your shaft as she kisses your balls. Then she slowly begins working her magic.
Oh...god... her mouth... it's better than you imagined. You never would have realized it before, but Riley has true dick sucking lips. And her technique... it's raw, unrefined, but what she lacks in refinement, she makes up for in gusto.
"Hurk Hurk Hurk Hurk...." she's fearless, forcing your dick against the back of her throat repeatedly. her eyes are watering and spit is running down your cock and her chin before long.
"Tell me baby... have you been with any guys at school? After you broke up with Matt?"
She stops sucking, stroking your dick. "Two guys, daddy. One was my RA's boyfriend."
"Riley!"
"I know, it was so bad, I blew him while he was on the phone with her and then he fucked me on her bed. She and her roommate were in Seattle for the weekend."
"Riley that's so bad... mmmf..." you can't help but be affected by her handjob. "Slow down, baby. I'm not a young man anymore."
"The second guy.... was my physics professor, Mr. Steinman..." she devours your head as you splutter.
"Riley!!!"
"I know, daddy... It was the night after my final. He had a beer with us at the Black Bear to celebrate classes being done. He's about your age, daddy... and he always reminded me of you.
We fucked in his car, and I swallowed two of his loads." She resumes her work, slower this time.
"Riley, fucking your professors is not acceptable behavior... you need.. you need to be punished..."
Her eyes burn with desire.
"I do.... I really do daddy."
Before long, the bedroom is ringing with the sounds of Riley's moans and grunts. She's totally naked, riding your cock with two hands squeezing your chest.
"You're so sexy, daddy. I love your new muscles... Oooh ooh ooh ooh ooh...."