Not so fun fact
Steve went back to a time when Bucky was still on track to be the Winter Soldier
Steve still had the super soldier serum and absolutely could have saved him
But he didn't
I do believe Steve deserved a happy ending to his story, but if I had the opportunity to save my best friend from being tortured, brainwashed, and made into a terrorist
I certainly wouldn't be wasting my time with an old flame I kissed one time. (I know their relationship is different in the comics but Im going off of the story the mcu presented us with) I can't have a truly happy ending until I know my best friend is happy too. And it's SO incredibly out of character for Steve in so many ways.
They had the opportunity to preface Steve's ending with a conversation with Bucky where a lot of things could have been explained but no. We are supposed to "assume" that conversation happened which is not only bad storytelling, but incredibly lazy and sloppy writing.
Steve did not act like a friend to Bucky in the end, he just left and didn't really do anything for him. That's what pisses me off about his ending. Make whatever excuse you want, friends who truly are friends communicate about that kinda stuff and the film's unwillingness to show that communication tells me they didn't care at all about these characters. Then for someone to go back in time enough to stop their friend from being tortured, brainwashed, and commit violent and unspeakable acts? Yeah no. Steve Rogers cared so much about not only true justice but Bucky Barnes himself, he never would have been content knowing his friend was going through a literal hell while he got to play house with Peggy (or whoever he married)