Castiel looks up toward the roof of the car, up toward the heavens in a gesture carried over from his time as one of the Holy Host. Searching for a Father who cared, brothers and sisters who listened, a plan that would work, that would save the world and the Winchesters in it.

Thou shalt have no other gods before me.

Castiel had already broken other commandments. What's one more?

"I will do whatever you ask of me, Dean." And ask nothing in return. True devotion is the only thing left that Castiel still understands without a single hiccup, and if Dean doesn't want him to go, doesn't want to leave, then Castiel will devote himself fully.