Cum in her pussy now, post-nut clarity later

Adam knew that nothing would ever be the same after this. He knew that cumming in his sister and possibly conceiving the Alabama delegation to the school would be much too fucked, but at this point he was (so to speak) in too deep. He had seen his twin sister naked, gotten hard over her, already slapped his meat across her face, and even explicitly and publicly admitted his fantasies for her. At this point, this is just the musky icing on the worst cake he's ever had in his life.

Not that his decision was made any harder (heh) by the physical exertions of the sin going on. The back-and-forth motion in Alice's juicy coochy tickled Adam's frenulum, producing a feathery touch to the tip of his schlong that he was quite surprised hadn't already burst. As he kept going, he noticed his sister was also getting a bit spasmatic , the walls of her birth canal (hopefully not of the birth of his child!) violently closing in and out of his member. Fearing that he'd lose his grip on her breasts, Adam moved his hands to a more stable position... her neck.

As Alice kept shaking, she noticed Adam's hands wrap around her neck and start closing around her throat. She was already on the edge, but this lightest of **** sent her over as she rolled her eyes in the back of her head and shrieked her pleasure loudly in front of the whole class. She noticed as she was clamping down on her brother's penis that it, too, burst as she felt the jetstreams of semen hit her cervix as Adam flopped his dick out of his nude sister and she fell to the floor, panting in her refractory period as she felt her brother's semen ooze out of her.

For Adam, though, there was no refractory period. As he plopped out his flaccid but engorged penis from his sister's vagina and started getting dressed, the full enormity of what he had done hit him. The shame from the sex act made his cheek flush as he was almost (just almost) as embarrassed as his sister still lying on the floor before him.