Dean was on a case where he was being punished for his guilt by a god.. the god spoke to him about you and how you idolized him when u were alive and was why you died for him.

so one of Deans guilt was not being able to save you so you were brought back by the god to kill him..

“you know he was right about one thing..” you spoke up to Dean standing across the room

Dean looked at you with affection in his eyes and a sad smile, “what like ur massive crush on me?”

you laughed and shook ur head, “as if.”

he stared at you with soft eyes as you laughed his smile faltering for a moment then back to a small sad smile.