It wasn't that Bucky had forgotten the basic things. Not the way he'd forgotten Steve, or the rest of his past before he'd been the Soldier. It was just...without mission parameters like "eat this many calories at this time" or "sleep for four hours at this time," he let the things his body needed get away from him. Just a few times. Just at first. Until he figured out how to listen to his body again. To identify "hunger" before it left him weak and shaking; to identify "tired" before he collapsed somewhere and slept for sixteen hours straight.
After he got the hang of those two, the rest was easy stuff. Showering, getting his laundry done, making sure to get the rent in on time—all the stuff you needed to do to be a person (or at least the kind of person who didn't draw the wrong kind of attention when all you wanted was not to draw any).
So he had the rest of it figured out for a few months before the itch started in the back of his mind. It took longer to figure out this need than the others; it too a couple weeks of growing more and more frustrated, certain there was something he wanted or needed to do, but not what it was—
His body had clued him in on food and sleep after a few days. It fucked with him for a lot longer this time, but eventually it let him in on the secret.
It was long past midnight, long after he'd gone to bed. When he woke up, he knew he'd been dreaming. Not nightmares, but of two people moving together in the shadows. Who they were, whether one of them was him, the other somebody else...he didn't know, and it didn't really matter. When he woke up, he was panting and sweaty, and so hard it hurt.
He'd had hard-ons since he got here, but morning wood was just annoying, something that would go away if he ignored it long enough, or took a cold shower. It didn't mean anything, not like this did.
Later, Bucky would think back, and he'd remember the time he'd woken up just like this when he was a kid; and he'd remember all the times, when he was a little older, that the itch had send him to try to find a partner to help him scratch it, if he could.
For now, he didn't try to remember anything. He just wrapped his hand around his dick, part of him relieved to finally have the answer to what had been frustrating him, but most of him completely desperate for a release that hadn't even occurred to him until now. Next time, he'd think about technique, but this time he just jerked himself, fast and hard as he could. He panted and groaned there in his own little apartment, the one he'd chosen for himself, the place that was almost starting to feel safe, even if there wasn't anywhere that really could be; his muscles tensed tight as stone as he got closer and closer to the edge; then, after not very long at all, he came hot over his fingers and stomach.
He hadn't remembered how loose he always felt, after, or the way he always fell asleep right away. But his body wasn't really looking for his input anyway, so he was already halfway down by the time his breathing slowed down all the way.
He wouldn't have been at all surprised to learn that, for the first time in a long time, he was smiling in his sleep.