One of the very few ~spoilers I heard before I saw this movie was that in terms of storytelling tropes, Sam Wilson’s role was very similar to that of a love interest. And you know what? It totally was.
Right from Sam’s introduction at the beginning of the movie, he’s instantly characterised as an appealing and fundamentally ~good character. It wouldn’t be an exaggeration to describe that park scene as a “meet cute,” with Steve being so drawn to Sam that he has to befriend him, and Sam being so open and receptive that he invites Steve to come visit him where he works. On their second meeting, Steve is impressed by Sam’s work as a counsellor for military veterans, and Sam and Steve almost immediately open up to each other about intensely personal aspects of their life: the death of Sam’s best friend, and Steve’s uncertainty about his life in the 21st century. This exchange has such an impact on both of them that Steve feels able to show up on Sam’s doorstep as a fugitive, and Sam is willing to risk his life to fight alongside him. The film ends with the implication that Sam is going to quit his job to go help Steve track down the Winter Soldier.