Human's had, on rare occasion, touched Castiel in some attempt at comfort. It had been meaningless to him in his borrowed body.
This was different, the touch of a brother, as it was in Heaven those rare times comfort was called for. Castiel relaxed into Aziraphale's body, his head sank to his fellow's shoulder. He would be unrecognisable to any human who new him but he didn't care. He clung to his brother as if he was the last branch keeping him from being swept away. He did not make any other outward signs of distress, merely clung there for a long moment before stepping back.
"Aziraphale," he said softly. For the moment he seemed unable to say anything else. Finally he managed, "It is good to see you."