"I closed my eyes in obedience. I felt a light kiss on my lips, where there was always a little fresh blood which never would go away. And then I fell asleep.
Next morning someone woke me: I had to have my wounds dressed. When I was finally awake I turned quickly to the mattress next to mine. On it lay a stranger I'd never seen before.
Dressing the wound hurt. Everything that has happened to me since has hurt. But sometimes when I find the key and climb deep into myself where the images of fate lie aslumber in the dark mirror, I need only bend over that dark mirror to behold my own image, now completely resembling him, my brother, my master."
-- Hermann Hesse, Demian
You wrestle him onto the bed - his breathing is fast, heart rate elevated, and his skin is slightly slippery to the touch. A higher baseline temperature than the average human; this has been mentioned many times. It is a mostly-useless detail that is generally unimportant to mission parameters, past or present. He is wearing pajamas, because it is two a.m. and you woke him up, having judged that the element of surprise would give you an advantage.
You have not misjudged the situation. You have been trained; you are very good at reading body language, and the way that Captain Rogers frequently stands closer to you than to other people, that he makes an effort to touch you as often as is feasible, watches you when he thinks you are not looking, are all parts of a puzzle that is not difficult to put together. There is a certain intent that is difficult to miss when you are searching for it. Once you were certain of what Captain Rogers wanted from you (from James Buchanan Barnes, rather), all that was required was a plan of action.
When you push him down, putting both hands on his hips to hold him in place, he goes abruptly very still. His hands clench into fists in the bedsheets as you pull his flannel pants down. You look up at him and he is looking at you with an expression nothing short of shell-shocked (shell shock: the reaction of some soldiers in World War I to the trauma of battle, a reaction to the intensity of the bombardment and fighting that produced helplessness). You smile with your teeth, a smile you practiced after seeing it in the Smithsonian, and mouth the bulge of his erection through his underwear. You have not misjudged the situation.
"Buck," he says to you. "What--?"
"Shh," you answer, hooking your fingers into his underwear and dragging it down. Not too far; you leave the briefs around his legs, restraining them slightly, though certainly the fabric would provide no significant resistance if he were to exert any strength against it. You don't bother with subtlety; you swallow him down, your mouth sliding along his cock until your nose is pressed against the skin of his belly. His hands touch your hair and shoulders for a moment - almost as if he wants to push you away but is uncertain and unwilling to risk hurting you (ridiculous, a gentle push from him would never be forceful enough to injure you).
You look up at him again and his eyes are closed. His expression looks almost like pain, now, but you are aware that sexual pleasure and pain often share coinciding physical appearances. His hands drop away again, balling up at his sides. He is silent. Perhaps you're not performing adequately.
You frown a little and concentrate on moving your mouth - varying the suction, working your tongue along the shaft. His hips jerk in response a few times and you focus on those areas, but no matter what you do, he stays quiet. His hands in fists. Resisting.
You let him slip out of your mouth with a wet pop and he jerks, opening his eyes for a moment and looking down at you. You don't smile at him this time; you just lick your lips and use your hands, still on his hips, to turn him over onto his stomach. For whatever reason, he doesn't resist that. He pushes up on one of his elbows and looks at you over his shoulder for a moment. You find this facial expression of his difficult to read; it's one you've never seen before, mostly perplexity, but part of it is something else, as well - something you can't define.
There's lubricant in the pocket of your pants. His breath speeds up when he hears the cap snick open. Anticipation and fear are hard to distinguish, physiologically. You think maybe you should have kept him on his back so that you could watch his face instead, but you also feel you have committed to this position at least for the time being. To turn him back over would reveal too much uncertainty.
Your hand is slick with lubricant. You push one finger inside Steve. He makes a sharp, shocked noise, but he neither looks back at you nor pulls away, so you work your finger in and out. He makes another grunt at the first touch but then goes silent again except for his ragged, labored breathing. You manipulate the angle of his hips a little with your free hand and slip a second finger inside him.
After two and one half minutes, the grip of his body has loosened enough that your fingers slide easily. You unbutton and unzip your pants, watching the dance of muscles tightening and jumping in his back as he breathes. Your cock is only half-hard (a perplexing malfunction) and it takes several strokes of your hand to reach a full erection. When you push inside his body, it is very tight, and he trembles. You think perhaps you have been remiss in not preparing him more thoroughly.
Still he makes no noise at all. You put your hands on his hips and guide them, steadying him at the angle that should provide optimum stimulation. He is very tense. His muscles quiver. You have not misjudged the situation; Steven Rogers and James Barnes have been friends since the 1920s. They were the most steadfast of companions. They were very close. Steve Rogers licks his lower lip sometimes when he looks at you. Sometimes he touches your face, strokes down the line of your cheek, neck, and shoulder, as if you are a frightened cat. He risked his life in the foolish endeavor of attempting to break your programming. He accepted you when you came to him. He let you into his home - a weapon, a dangerous tool - and he does not lock his bedroom door at night to keep you out. You are very good at reading body language. You would not have made a mistake about something so crucial.
The minutes pass by; you count seconds in your head. Captain Rogers does not reach orgasm, and neither do you. Eventually the friction starts to irritate, so you pull away. He stays exactly where he is, face down on the bed. You pull up your pants and back toward the door, not turning away in case he decides to retaliate for your unsatisfactory performance.
He doesn't move. You go to your room and lock the door behind you. You lie awake for the rest of the night.
Several months later, when your brain has recovered enough from years of trauma that your memory is no longer a blank, empty void - months later, when you can see around the holes in your consciousness enough to start to develop a framework for who James Buchanan Barnes used to be - you start to realize how epically, how catastrophically you fucked up.