Grace having a vivid wet dream and being really embarrassed about it when he wakes up
Simon being a light sleeper who was awake the entire time Grace humped his ass and mouthed at his neck until he came in his pants
i already see simon as a perpetual little spoon (something something curl up in ryan gosling's arms) so this setup is perfect
simon is used to waking up when grace has bad dreams, so when he's roused by the sound of grace mumbling and softly moaning, he's prepared to roll over and wake him up to comfort him. grace shifts, but instead of trying to fight off an invisible attacker, he grinds his hips against simon's ass and simon freezes. he recontextualizes the sounds grace is making and... yeah, no, those are definitely sex noises.
grace's hands grope aimlessly at simon — his chest, his stomach, his waist — as he buries his face in simon's shoulder. he opens his mouth, panting breaths warm against simon's skin, and presses it down in a half-kiss. simon blushes, and as grace continues his uncoordinated grinding, he can feel himself getting hard. he panics a little; is it okay for him to be turned on by this? would it be okay to slide a hand beneath his waistband?
"simon," grace whines in his ear, and simon bites his lip to muffle a groan of his own. he wants to turn around, to give grace a little more friction to work with, but he's afraid he'll wake him up and ruin the moment. instead, he holds still and lets grace rut against him until he feels his hips stutter and hears him gasp and knows that he's coming.
grace is still for a while. simon assumes he's asleep, that his fun dream has ended, until grace whispers, "you awake?"
"ohmygod." grace rolls away from him onto his back and covers his face with his hands. "i'm so sorry, simon, that was —"
"what were you dreaming about?" simon interrupts, rolling over to face him. he smirks a little as he adds, "sounded like you were having fun."
simon scoots closer and kisses his cheek, his noise, his mouth. "c'mon, ryland, let's have a little more fun."