Steve froze when he saw Bucky's form appear from the shadows. Everything inside him stilled for a few seconds, and only when it all stopped, did Steve realize all of the raging ball of roiling anguish he had been carrying since the day he watched his friend fall for the second time. He stood there, unable to fully appreciate the few moments of peace granted to him when his mind decided to finally be blessedly quiet. He couldn't move, and Bucky wasn't the only one who felt like he couldn't breathe. It wasn't paralysis. He didn't dare move, lest Bucky might fade away like a mist.
The apparition came closer, and Steve felt like he was screaming inside. He swallowed nervously, but still didn't lift a finger. Only when Bucky was standing right in front of him, only when he spoke, did Steve feel his chest spasm as his lungs screamed for air. Steve. The last time he'd heard Bucky say his name the man had dissolved into dust right before his eyes.
That image had broken Steve. Nobody could probably understand the weight of unresolved conflicts and feelings between the two of them, even though a few had guessed at the depth of said feelings. It was much more complicated than attraction, or the love that dared not speak its name. They were family. Steve was a very different man now, blessed with the clarity tragedy tends to bring. He coughed as he choked on breath and the words that wanted to come out all at once. His eyes watched Bucky remove his cap, lingered on the way his hair came down over his cheeks. Steve's face twisted, jaw muscles jumping.
"Buck," he ground out, huffing out a breath as his stomach clenched in a very visceral reaction. He was here. He was alive. And then he had an armful of Bucky. He was there, strong, solid and vibrant. He could feel Bucky's heartbeat, and the tears he'd barely been holding back for weeks and months just poured out of him all at once. Steve was glad Bucky had received a version of the super soldier serum, because he could feel the terror of loss driving his brutal embrace of his oldest friend. He too would have probably crushed a regular human, but he couldn't let go.
"I couldn't stop him! I'm sorry. I'm sorry," he sobbed, blinded by tears as he took in the smell of Bucky's hair against his face, his skin, the rasp of his stubble on his cheek. "It's you. It's really you," he whispered, thanking any deity who might be listening who might have helped make this happen. The core of Steve's profound guilt; because of course he blamed himself for not stopping Thanos and allowing Bucky to die; came pouring out of him in sobs and tears until he wasn't sure who was holding who up.
Most likely, they were holding each other up, like it had always been.
After what felt like an eternity, Steve pulled back, cradling Bucky's face in his trembling hands. He gave his friend a shaky smile, and said, "Hi." After which, he promptly started crying again like an idiot. Behold, the mortal who went toe to toe with Thanos, who looked the Mad Titan in the eye and didn't flinch, reduced to a blubbering fool by the sight of his not-dead friend.