Castiel sat by the side of the bed with a small smile on his face, watching Dean sleep, and wondering when it all became so clear; Hunt monsters. Save people. Protect them, no matter what.
Though he was now human, sleeping was not something that came naturally to him, he had to either drop from sheer exhaustion or be knocked unconscious to take a break.
He could remember quite clearly, how after he had lost his powers, he had given up, stopped wanting to live. Didn't eat, didn't drink; until he discovered whiskey, that is.
Dean and Sam, the ruthless Winchester's took care of him, they cooked him meals and they made sure he couldn't find the scotch.
They kept him alive.
And now he had to repay them.
The Winchester's needed a guardian angel but for now, they would just have to settle for him.