"It's not your fault, Dean," Castiel assured as he coughed up blood while he laid next to Dean. The situation vaguely reminded him of when he was too weak to fight off Raphael. Then again, the fight against Raphael was physical, mostly, while the fight with Naomi was a mental battle. Unfortunately, he had lost the souls that Crowley had loaned him and the subsequent power from them, and he definitely didn't have the power from Purgatory anymore, so he stood no chance against Naomi.
Except when she told him to kill Dean.
"That bitch," Dean ground out as he tried and failed to hold back tears.
Yet again he was about to lose someone. Yet again he had failed to protect. Yet again he was being left alive while someone more important, more useful, was about to die.
"No, Dean," Cas whispered as he reached his hand towards Dean's shoulder. The grip was surprisingly strong, Dean thought, for someone who was bleeding out.
"I thought we agreed that you'd stay out of my head, man," Dean murmured. His shoulders fell and once again he saw himself as the weak one.
"You are useful, more than you know. And –" Castiel had to pause to cough up more blood. Once the coughing fit had stopped, and after he reached up to wipe away Dean's single tear, he continued. "I've seen many things. I've seen your whole life. And you haven't heard it enough, but at least know that I'm proud of y-" Castiel started coughing again, and this time, his breathing stopped.
"Cas, no," Dean begged. He had taken the knife out that Castiel had stabbed into himself to stop the compulsion, and he thought he had staunched the bleeding well enough for Cas to live.
Apparently he still wasn't good enough. Apparently he was right.