assetandmission:

(x)

When Bucky was missing in action, Steve thought he was dead. But it’s interesting to consider that Steve went missing, too, and Bucky didn’t know what had happened to him. 

Steve signed up for a secret government experiment. I doubt they let him have contact with anyone he knew, or tell anyone where he was going. And when he became Captain America, his real identity was hidden. So Steve Rogers just disappeared. Letters from Steve must have abruptly stopped. Bucky would have thought something terrible had happened to Steve, like he was arrested for forging documents, or he picked a fight with the wrong person. Maybe Steve wrote Bucky once, to say he was accepted into the army, and then Bucky never received another letter. He would have assumed the worst.

In this moment, it looks like Bucky is realizing Steve is really alive.