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Sam didn’t care that Dean slept around so much because at the end of the day, she was still his number one girl— the only one who mattered, the only one he truly loved and cared about.
So imagine her surprise when Dean gets a girlfriend. Like an actual girlfriend. Not some sex-on-a-stick whore he fucks, but a girl he takes on dates where they don’t do more than kiss.
The girl’s quiet, mousy, and bookish —she’s basically Sam without the Winchester, and boy, does that just piss Sam off.
Is Dean trying to replace her? Is he sick and tired of her? Is she not good enough for him?
One night, Dean brings the girl over to the cabin they’re staying at (barf) and she has the gall to gush all over Samatha.
“Dean's told me all about you! You’re just as cute as he says! Dean just adores you! Blahblahblah.”
Sam zoned out three sentences in. Sam kept staring at the girl, whose name Dean told her like eight times already, but she didn't care enough to remember, thinking and thinking.
“What does she have that I don’t?”
“Why is Dean dating her?”
“I wonder if she’d run for the hills if she knew her boyfriend was fucking his little sister?”
Hey, look at that. Lightbulb moment.
It’s about 3am, the girl is sleeping in Dean’s arms, both of them having dozed off on the couch during a movie marathon. Sam tiptoes out of her room to wake Dean and spiels some bullshit about how she had a nightmare and how she has to have her big brother cuddle her to sleep.
A 20 year old man cuddling his 16 year old sister to sleep is a little weird, but it’s not incest weird. Dean could probably make that girl forget about cuddling with a charming smile and a half-assed excuse. Sam wanted something more extreme. Something that couldn’t be explained away, no matter how taken this girl was with Dean. Sam wanted to lay her claim on her big brother.
Dean gives in, obviously which ends up with the cuddling in Sam's little twin bed. “Go to sleep, babygirl,” Dean murmurs, his arms wrapped tightly around her from behind. “No more nightmares.”
Sam hums something in acknowledgement, squirming around until she’s nose-to-nose with Dean.
“Dean…” she murmurs, brushing her lips against his. He’s such a sucker for her.
“C’mon, you know we can’t…she’s right outside…” Dean whispers but his eyes betray him, tracing Sam’s lips.
“She won’t find out…come on, please?” Sam pouts and gives Dean the puppy eyes that work oh so well. “Just a quickie. I need you.”
“Ok…” Dean brushes a stray stand of hair from her face. “But promise me you’ll be quiet, ok baby?”
“Ok, Dean,” she whispers against his lips. Her hands are eager and quick, freeing his hardening cock. She makes a big show of licking and slobbering all over her palm like an animal, using it as lube to stroke him.
“Fuck, baby…” Dean groans, his eyes literally roll to the back of his head. “You’re so good f’me, hm? My perfect little sister.”
“Yours,” she murmurs as she swings a leg over his thigh. She drags his cockhead along her wet slit, teasing her throbbing clit. She stopped wearing panties to bed a long time ago, when Dean and she started fucking regularly. He appreciates easy access. See? She is a good little sister.
Wasting no time, she sinks onto his cock and Dean’s eyes flutter shut, flourishing in the welcoming wet warm heat that is his Sammy.
“Oh, Dean!” She moans loudly. On purpose. Trying to sound as pornstar-y as possible.
“Sam-” Dean’s eyes fly open. “Jesus, shut up,” he grips her hips tightly, halting her movements. “If you won’t keep quiet, we can’t do this.”
Sam resists the urge to roll her eyes. Oh, so now he cares about getting caught — where was this attitude when he throat-fucked her until she was choking in that gas station bathroom and there was definitely a guy in the other stall?
“Sorry,” she mumbles, not apologetic in the slightest. “Just slipped out.”
He sighs but his grip loosens and she continues fucking him. He lets her do all the work; it’s obvious she needs this more than he does.
Both of them are biting their lips, trying not to make a sound. It’s hard for both of them— dad’s gone so often, they’re just used to fucking each other however they want, as loud as they want. Dean's trying not to wake his girlfriend up. Sam doesn’t want Dean to pussy out.
As quiet as they try to be, the unmistakable sounds of sex are still there: Sam’s wet pussy, the bed creaking, their thighs smacking together.
Jesus, this girl must sleep like the dead, Sam thinks.
“Oh, Dean,” she tries again. Not loud, but not a whisper either. Like an inside voice volume.
“I got you, baby,” he kisses her so deeply and so lovingly she almost forgives him getting a girlfriend. “Are you close? Are you gonna cum for me?”
“Yeah,” Sam whimpers. “More, I need more…”
“Greedy little thing, aren’t ya?” Dean chuckles. He slows down, which makes her whine a little. Dean slips his throbbing cock out of her, leaving her feeling all empty and cold. He sits up, back against the headboard as he gestures for her to sit on his lap.
Sam sinks down onto her brother once more, riding him. “Deandeandean,” she gasps as she picks up the pace, bouncing on his cock like the grade-A whore he’s trained her to be.
Sam can vaguely hear the sound of the floorboards outside her room creaking.
Oh. She’s up.
Sam wraps her arms around Dean’s head, her fingers lacing tightly around the back, feeling his short and sweaty strands. She shoves his face into her chest, prompting him to lick and suck on her perky tits through her thin night shirt. Dean's eyes are squeezed shut in ecstasy. Her tits were probably his favourite part of her. Right after her pussy.
“Dean. Dean,” Sam moans, getting louder and louder. Dean's too distracted to notice the sound of the door creaking open.
Sam looks over her shoulder at the door, seeing the wide and horrified eyes of a girl discovering who the Winchester kids really are.
Sam grins.