Detailed further in Captain America's page, but Bucky's first birthday as Captain America. It wasn't the best time for the Avengers, but everyone got together to help Bucky celebrate for the first time since WW2, with Natasha teasing him for his age by placing near enough ninty candles on his cake. Before he blows them out, Mockingbird stops him to ask if he has any wishes to make first, and he responds with, basically, nope. For the first time, he's happy with his life.
Pretty much everything about Bucky and Natasha's relationship, before their controversial breakup. The two fell in love during their time as Soviet pawns, and were so infatuated that their relationship began breaking down his programming, and the sight of what they were doing to him disgusted Natasha so much that, if not for her own brainwashing, would have likely made her defect. Decades later, they meet up first as enemies, but once they're on the same side Natasha takes it upon herself to help him settle as the new Captain America, and the two basically agree that time as KGB assassins was pretty shitty, but they always remembered their original affair as the one good moment of it, before reuniting that relationship.
To a lesser extent, his relationship with Sam, The Falcon. Sam originally doesn't see him as anything but Steve's disturbed former partner, but goes out of his way to protect Bucky in order to honour Steve's death. The two become such good friends from all of this that Bucky ends up considering him his best friend, besides Steve of course.