The longer he feeds, the stronger Castiel feels. That weakness is already ebbing away to be slowly replaced by a feeling of strength that he can at least tell is supernatural by nature.

Dean grabs his coat and Castiel realizes that he wants more. Why should he fight this hunger when he's finally found the cure?

He leans back in easily and he pushes himself up and over until he's straddling Dean's thighs, lips meeting Dean's again.