So I sort of have this headcanon where everything that came as a choice to Steve was forced on Bucky, and that’s the difference between them.
Steve got the choice to join the army, Bucky got drafted.
Steve chose the serum, Bucky had all those experiments forced on him by Hydra.
Steve chose to stick with SHIELD when he was unfrozen, and he battles with that choice through all of TWS, but it was still his. Bucky never had a choice at all in anything he did as The Winter Soldier.
And even before all that, way back when they were just kids in Brooklyn, Steve had a choice to keep getting into fights. He didn’t have to stand up for what was right, even if he thought he did because no one else was. He didn’t have to get his face punched in every other day. But Bucky never had a choice in pulling him out of those fights.
'Cause Bucky never even had a choice in loving the damn kid either.