HYDRA's methods of training and programing the Winter Soldier were a mystery to many. What most people didn't understand was that a lot of what he could do came from him, not just his programming. The fighting, the marksmanship, that was all learned behavior. He'd been forced to learn it, but it wasn't something they just put in his head. And that included languages. Bucky, along with the other Winter Soldiers that had been created, all had been made to learn more than two dozen languages due to the nature of their missions. They were put into situations all over the world and had to adapt as necessary. Even though he never actually interacted with people, he had to observe, listen, and understand what was happening around him and therefore had to be fluent in multiple languages to do so. American Sign Language had been on the list to learn, though it was more for his own sake and those he might be operating with on missions. It was for stealth purposes. As the Winter Soldier, he was often a long range assassin. If he was working with someone, he could watch, they could sign to him where his target was heading and he could hit whoever it was without a word being exchanged. It was efficient, to say the least.
Now, he had a much better purpose for that knowledge and he was grateful he had it. Bucky hoped that using a language Clint understood even better than the spoken word would show him that this mattered. It wasn't just about how he felt about Natasha. Clint was just as important. What they'd been building between each other really meant something to Bucky. Clint meant something to him. More than a little something.
He watched as Clint signed back to him, and basically confirmed that this hadn't been one sided. It was a bittersweet feeling, similar to how it felt when Natasha told him she loved him, too. It was wonderful, knowing he was loved by her and that he hadn't misread what had been going on between him and Clint. But the sad part was, that even though he'd been open and honest, and corrected himself so he didn't make the same mistakes he made with Steve, it still left him... well, alone. Happy for them -- genuinely, truly, happy. But alone. It was an outcome he expected -- Bucky did not think himself so highly as to even consider the idea of coming between them in any way. That wasn't his goal, and never could be. He wasn't hoping for anything out of this. But it still hurt, knowing that even when he tried to do right by being honest, he was going to end up alone.
"I know," he replied. "I do know." After this, after being so open and honest with three people and saying more in those conversations than he had since before World War II, Bucky was tired. Tired, but knew he couldn't just hide himself away again as he'd done with Steve, or else it'd cause worry and he didn't want Clint and Natasha to show up at his door again having to practically peel him off the floor to bathe again. Bucky didn't want to get that low. So he had to carry this the way he carried everything else, and just keep moving.
"I just thought you ought to know," he said. "I hope I'm still your favorite mythical creature." Salvage this by making it light again. Because what else was there to do? It wasn't going to change anything to dwell in the fact that yeah, they liked each other but that was as far as it could go.