Dean looked at Cas and saw the pain on his face. He shouldn't have asked him to leave. Cas got up and turned to walk away but not before Dean caught his arm. His angel turned and looked at him with a Cas-style head-tilt. Dean couldn't help himself, he took his hand in both of his. "Please... Stay," he muttered. Note: spoilers through season 13! Update: Chapter 50 is up!

Castiel is newly human and living in the bunker. Dean is just trying to be a supportive friend, but the closer he gets to the former angel, the harder it becomes to avoid what has always been simmering between them... S9 Destiel, canon up until the angels falling but branches off after that, slow burn (well, detailed and sluggish but let's call that slow burn). Multi-chapter.

Castiel is an omega whose body has begun to reject suppressants after twelve years of continuous use. Faced with a hysterectomy or using an alpha service, he chooses the latter as much as he loathes the thought.