Steve stops right as Bucky's going into full-body shuddering and unable to string a proper sentence together. He pulls off of Bucky's dick with an obscene pop and looks up at him, grinning. Bucky looks livid, and he strains at the cuffs Tony made for them (and gave them in front of the other Avengers with a loud insinuation that they'd get a lot of use out of them and their newly-reinforced bed). Steve pats his thigh and sits up.
“Not yet,” he says cheerfully.
“Bastard,” Bucky chokes out, still shaking. “Fifth time you've...fuck.”
Steve's face softens for a moment.
“Are you sure you're okay with—“
“'M fine,” Bucky gasps with some difficulty. “Asked you to. Don't worry.”
He throws his head back and just breathes heavily, eyes closed. Steve waits until his chest stops heaving and he stops pulling at his restraints, and then he gets the lubricant from the bedside drawer. In a flash of inspiration, he squeezes more than he'll need onto Bucky's stomach, and Bucky jumps when the cold liquid makes contact with his flushed skin. Steve swipes some of the lubricant off of him and slicks up his fingers.
“If you're good,” he says playfully, “I might let you come this time.”
Bucky doesn't respond, but he cracks an eye open to watch him. He already looks wrecked, with long strands of hair stuck to his forehead and a thin sheen of sweat covering his whole body and skin reddened all over. Steve pauses for a moment, just taking in the sight of it, and Bucky shifts on the bed.
“Are you gonna—“ he starts, but Steve cuts him off.
“I'll do what I want at my own pace, thank you very much,” he says sternly, but he's smiling.
He opens Bucky slowly, carefully. They've done this many times before, but Steve is still always afraid of hurting him. He's aware that it's a near-perfect reversal of their circumstances before the war, when it was Bucky prepping him with more care and time than necessary, and it makes something in him hurt when he thinks of how Bucky is the delicate one now, despite and because of everything that has happened to him.
Bucky groans at the intrusion, straining to push down more on Steve's fingers. Steve holds him down with one hand and pushes three fingers in slowly, methodically. Bucky is panting and shivering by the time Steve gets them in and starts to thrust them minutely in and out of him. Bucky's plenty stretched already, but Steve keeps at it for another few minutes, just to get him really riled up. He makes sure not to hit his prostate, so every thrust is good, but not good enough.
“Please,” Bucky croaks, and that's when Steve knows he's ready.
Steve lines himself up and pushes in, slow and steady even though he doesn't really need to be careful. Bucky curses and tries to wrap a leg around his waist, but the restraints stop him before he gets very far. At least, that's what Steve assumes he's trying to do, because he always does it when Steve fucks him. Steve kisses him hard on the mouth and starts to move, languid and willing to do this all night if he has to. Bucky's babbling now, curses and Steve's name and pleas for more. Steve thinks about telling him to stop, knows he would stop if Steve threatened to leave him shackled to the bed and unsatisfied for the night, but it seems a little cruel. Instead, he muffles the noise with his lips and tongue.
It doesn't take long for Bucky to get right up to the edge again. Steve feels it when his body starts to clench around him, and he stops, debating. Bucky all but howls in frustration.
“Please,” he rasps.
“Please what?” Steve asks innocently, feeling a little bad but wanting to play this out for Bucky.
“Please let me come,” Bucky chokes out, eyes closed and throat bared.
Steve kisses him on the throat and starts to move again.
“Go ahead,” he says gently. “You've earned it.”
Bucky nearly sobs with relief. His orgasm is messy and perfect, wracking his body with shudders and painting his chest white. Steve follows him almost immediately, because Bucky isn't the only one who's finally getting to come, and when he pulls out, Bucky whines at him, exhausted but still greedy for more. Steve just scans his thumb print on the restraints (they're set so only he or Bucky can release them) and releases him.
Steve gets a warm, damp towel from the bathroom and cleans him off, murmuring praises and telling him how beautiful he looked. Bucky melts into the touch, sated to the point where he's unable to speak, and when Steve lays him back down on the bed so they can sleep, he clings to Steve like he's the only thing left in the world.