Cas shuddered and drew his Grace back, his hand hovering in the air by his friend's face. He was almost afraid to touch. He was not so gentle or tentative in his speech, however. "Sam... you should be dead from this. The extent of the damage..." He shook his head a little, his eyes skating over the hunter's broad frame. He thought, when Dean had called him before, that he'd healed Sam at least somewhat, but examining him now, that was hard to believe.
"Sam," Cas breathed his name out. "There are... other angels, ones whose job is to heal. I'm not one of them; I don't know if I can..." His eyes caught Sam's again and he cut off, his mind suddenly flashing back months and months - Sam and Dean and Bobby, Cas put his hand on Sam's head, reached in with his Grace and tore, the wall collapsing like... tin trying to hold back molten lava, and Sam dropped - his fault, his doing, but it was necessary, he needed to distract them, and it would be okay, he was going to fix him - Cas was going to fix him. He'd done it before, clearing Sam's head and taking on his pain. But it wasn't enough, it was never enough. There was always some new hurt to heal.
Cas bowed his head for a moment in thought. "I might... I could bandage it somewhat, I think? It's more... more healing the symptoms than the cause. But it should help." He raised his gaze to meet Sam's, his vessel shrinking in on itself with hunched shoulders.