[Perhaps if John hadn't just told Bucky fairly recently about what happened to Sherlock, that might sound comforting. But it doesn't. He reaches over and lays a hand on Clint's arm, frowning, and shakes his head.]

Calm down, John.

[It's an order, rather than sympathy.]

He's not going to do that here, you can watch him. But you can't take responsibility for his actions because you feel guilty for what happened before, he makes his own choices.