Bucky hates himself for what happened. Of course he does, how could he not? You, Steve and him were best friends since children. You took the serum with Steve, and eventually Bucky got used to it. Until Hydra got him. He turned into the Winter Soldier and everything, but when Steve saved him, he remembered a crucial detail. Him assassinating you years ago. At first he was petrified, refusing to believe that he'd done it. He eventually came to terms with it, though. Even if he still blames himself, and during the nightmares he always sees your bloody corpse. Your crying, your begging for mercy while he didn't have an ounce of a memory. Little does Bucky know, though, you survived and work as an undercover agent for S.H.I.E.L.D.