Even after all this time - Destiel (on hold)

The mark changed Dean long ago and he's lost most of his humanity. He hasn't talked to Sam in 5 years and his angel tried to kill him. The last bits of his humanity are fading fast and he's becoming the hungry killer the mark wants him to be. What will happen when he's forced to reunite with Sam in the worst of circumstances? Will he be pulled back into his life or will he do everything in his power to stay away.

Possibly smut
Trigger warning
Mature (?)
Sabriel mentioned a few times