Dean could hear the sobbing a few yards away, even before he was right in front of the door to their motel room in Nowhereland, USA. It was Sam. Dean could always recognize that sound, even though it didn't happen often these days. He knew that Sam…well, guys in general, don't like it when people come in while this is happening, because they can hear it from outside. But he goes in. His DNA tells him that he needs to get in there. So he unlocks the door, and slowly opens it. The room is pitch black, even the alarm clock was unplugged from its socket. Dean can't see anything.
"Dean, just go. Please. PLEASE. Just go. Get out of here. I don't want you here. Go. Please. Get out of here." The words came from a broken voice that was drowning in tears.
All Dean can make himself say is "Why?"
"I don't want anyone here. Please just go. Leave me alone. I don't want you here. I DON'T WANT YOU HERE. PLEASE JUST GO." There was no anger. Just desperation and misery.
And Dean leaves. He closes the door behind him, and pockets the key. Sinking down right outside, the beige and green wallpaper is smooth enough to carry him right to the floor. But like hell is he leaving. He will not move from this spot, even if he can't go in. His hands cover his face as the sobbing keeps going, unbroken and unending. He can hear that Sam is trying to muffle the wails and cries coming out of his mouth with a pillow, but it makes no difference. Sam simply cannot control them. Dean wants so badly to go back in. To take anything and everything that Sam says or does like a silent ghost and just being in there holding his little brother. But he doesn't. Because Sam didn't want him to.
And while his face is in his hands, he feels Castiel appear beside him. The angel pauses a second, assessing the situation. He then says, "You are a true brother if you are feeling this. No true sibling can stand the sound of their brother or sister in distress or pain. It is unbearable to them. What you are feeling is right, Dean."
And Dean, guiltily, miserably, actually allows himself to draw comfort from this.