Jim’s not sure when exactly it starts, but one day he’s pressing Bones into the bed a little harder than usual, his fingers squeezing a little tighter, the marks left behind a little darker, and they both love it a little more than they probably should.
"More," Bones tells him breathlessly, his face flushed and his pupils blown dark. He tilts his hips up against Jim’s, erection right and straining inside his Academy-issued briefs. He still has his red tunic on, pushed up hastily above his heaving stomach so that slick skin meets skin. "Jim- please-"
He moans when Jim tightens his grip on his wrists, pushing them up beside Bones’ head and holding them there.
"Damn, Bones," Jim whispers, awe-stricken. "Look at you." He bends his head, licks a stripe up Bones’ arched throat and tastes the low groan as it rises from the other man’s chest. "Goddamn."
Bones lifts a leg and hooks it over Jim’s hip, dragging their groins together impatiently. “Get on with it,” he growls, his hair wild and his pulse fluttering beneath Jim’s mouth. “Or I’ll finish without you.”
Now there’s a challenge Jim’s never backed down from, and he shoves a knee between Bones’s legs, meets the eager upward grind with his own. “Jerk,” he mutters, grinning helplessly as he bites at Bones’ jaw. “You’ll be sorry for that.”
"Make me," comes the rough whisper against his ear, and Jim’s never been more happy to follow a command.