The story arc of Steve Rogers and Bucky Barnes is a heartbreaking one. From thinking that his best friend had died on a mission decades before to discovering that he had been brainwashed and used as a hired assassin by Hydra, to having to fight each other to near death, it’s been a ride.
These two have an unbreakable bond, though, which is clearly shown in a little scene during Avengers: Endgame. Bucky is the only member of the team to say a proper farewell to Rogers before he heads off on his time travel mission. It seems that Bucky was the only one that Rogers told about his plan not to come back and to live a life with Peggy Carter instead. We’re glad he did, though.