“Happy birthday, Sammy.”
Dean whispers it in his ear as he thrusts long and slow into Sam, more than enough stimulation to get him circling in on orgasm normally, but there’s a third player tonight: Dad. They’re both shoved inside him—Sam still can’t figure out how they both fit without ripping him in half—and the agonizingly slow rhythm they’ve had to adopt to keep from hurting him isn’t doing anything but driving him crazy.
Sam has only seen Dad naked once, he came home late from the library and found Dean facedown with Dad’s cock splitting his cheeks. It was still a shock seeing him whip it out, knowing it was going to go inside him along with Dean’s much more approachable length and girth.
Dad holds his hips, moves Sam in his lap with the kind of gentleness that doesn’t fit what they’re currently doing. Sam’s vagina aches, he’s going to ache worse when they pull out of him and leave him gaping, like his body would want to be filled again. While he accepted that Dad wanted to join them, he really wished deep down that it’d just be him and Dean on his birthday.
Eighteen, finally legal, and he’s celebrating by letting Dad and Dean tear him apart.