I know a lot gonna hate me for saying this but what Sebastian said about Steve's endgame ending what Bucky wanted for Steve what Steve wanted for Bucky makes a lot sense to me than Russos and writers explanation which was confusion where Sebastian put up a clear picture of

Both characters.. Let's face the truth Steve Bucky always be friends but they changed a lot over the years their relationship evolved of 70 years they became different persons with different wants.. Sebastian saw that clearly and i can see it now..

Although they still fucked with Peggy's past without explanation