Prequel
There is no light without dark. No warmth without cold. No life, without death.
Bucky and Steve throughout all the many stages of their lives (not counting those spent without consciousness or autonomy) have been mutually sustaining each other, body and soul, completing each other. When Steve was young and sickly, Bucky was what grounded him. They started to grow up, Bucky pulled Steve's ass out of every fight. They go to war, Bucky is his sniper and daily reminder of what Steve is so desperately fighting for. Bucky falls from a train, Steve crashes a plane. They both know the bone-chilling nihility of the ice. Steve wakes up, and can't remember a purpose without the presence of the person who kept him whole, kept him alive, for so long. Then, on a bridge in D.C., everything changes. Steve devotes himself to finding his long missing counterpart. Then to helping his friend remember himself, find his way through the labyrinthine ruins of his mind, recover from the unspeakable horrors and ghosts that haunt his past.
Bucky knows that nothing can remain beautiful like it is now. It's not perfect. It never could be. But it's so damn close to that Bucky sometimes has to fight back tears, because he lives in a world where he can be with the man he loves, he doesn't have to suffer silently when the memories flood and overwhelm him, he can exist, and be happy. Bucky has never been one for religion, not after the bible-thumpers that made him feel like some kind of degenerate, but he nearly fucking believes in God when he looks at Steve on the other side of the bed in the soft morning light.
Bucky knows that nothing this good can last very long. Steve, ever-hoping as he is, says that those thoughts are just part of Bucky's PTSD, invasive, intrusive thoughts that stem from survivor's guilt. Deep down, though, in the dark parts he doesn't acknowledge, Steve knows that he's not wrong.
Deep down, everyone knows that in a world full of suffering, near-perfection can never last.