Okay there's this one specific Godstiel fic that I just can't seem to find. This is the scene that sticks out in my mind. It begins the same as most Dean/Godstiel fics where Dean submits to Cas to save Sam and Bobby and fix Sam's mind.

Crowly agrees to help Sam and Bobby reopen the portal to purgatory and gives up a deal he made for the soul of a virgin in exchange for her blood.

FOUND! Link in Comments