Bucky knows that it's true the moment Clint walks through Bucky's apartment door, because Clint almost never comes to Bucky's floor without explicit invitation, and he never lets himself in, despite having the digital equivalent of a key.
Bucky would know even without that, though – it's written in Clint's betrayed, closed off expression, the hunch of his shoulders and the way he comes to a stop a few feet into Bucky's place, like he doesn't know what to do with himself.
"It's true?" Bucky asks, for want of anything else to say.
Clint nods, says, "He's alive," in an utterly flat voice. Bucky still can't always get his head around the future and being a person, but Clint may actually look worse than Bucky thinks he did when he realised Steve was alive. Bucky knows how to do this part, with a careful hand on Clint's shoulder, steering him into the living room and down onto the couch, where he huddles against Bucky with a small, wounded noise, and Bucky holds onto him and lets him shake and shake, like maybe he won't ever stop.
Natasha told Bucky a little about Clint and Loki, back when Bucky was first in the Tower and completely not ready to go see Clint, and then Steve told him about one of the agents who died, Coulson, that he was close to Clint and Natasha for a long time. Clint doesn't talk about Coulson, or at least he doesn't talk about Coulson to Bucky (some days, Bucky finds Sam and Clint sitting close together on the roof of the Tower, leaning into each other and talking too quietly for even Bucky's hearing to pick up. Those are the nights that Clint knocks Bucky's door and curls close in his sleep, and Bucky doesn't ask because that's part of how Clint and Sam make sense to each other, just like Natasha's turned out to be Bucky's kindred spirit in all things Russian mind-control).
"He said that he was glad to see me," Clint says. "That he's glad the Avengers are sticking with the new SHIELD and... I don't know why he didn't call before. I don't think it occurred to him."
He sounds exhausted and defeated and under all of that, just sad. And maybe Bucky shouldn't ask, but also maybe it needs to be said, and Bucky's going to have to be the one who says it. "You and Coulson – you were together?"
"Yeah." Clint smiles, which looks like it hurts a lot. "Not so much towards the end, cause he got kind of serious about the cellist, but for a long time before, yeah. Not – we were friends, but we..." Clint trails off into a vague yet explicit gesture. "I thought we were friends," he adds. "Maybe I was wrong."
Bucky understands feeling like the best thing you can do is stay away, except he doesn't understand what Coulson did, because Bucky managed a few weeks after he realised who he was, and then he just wanted to go be with Steve. And he wasn't even like that with Steve; he can't imagine just walking away from someone without a thought.
"I'm sorry," he says, because he wants to say that the Avengers don't have to work with SHIELD, that they don't have to work with Coulson, that they can go kick his ass if Clint wants, but he knows Clint well enough to know Clint will feel like he has to defend Coulson if Bucky says any of that, and this is a mess already, without Clint feeling like he and Bucky wound up on opposite sides somehow.
Clint closes his eyes, leans his head against Bucky's shoulder, and says, "I miss him," his voice gone small like he's afraid of the words. Like he's afraid Bucky's gonna laugh or something, even though Clint held onto Bucky while he cried after Steve told him about Peggy, how she wasn't dead like Bucky figured, just slipping away, and never said anything about how Bucky ought to be grateful she wasn't gone completely.
"I know," he says quietly. He tips his head, just enough to rest his cheek against Clint's hair, and it takes a while, but eventually, Clint sighs out a long breath, some of the tension easing out of him, and Bucky figures that, even if he doesn't really know what he's doing, he must be doing kind of okay here.