Castiel had taken to wrapping his arms around Dean's front, whenever he could, whenever it was even mildly appropriate.
Sam thought it was cute, the way the fallen angel would cling onto the blond hunter, resting his chin on his shoulder, just inhaling his boyfriend's scent.
Dean had been startled at first, not sure what to do, but eventually he worked out that the best thing was to just let it happen. He enjoyed it, having the ex-angel in such close proximity, and being held by the strong arms. He'd never admit to liking the latter, of course, but, in his mind, his own private place, he could admit to it.
After about half a dozen times of Castiel's back-to-front hugging, the blond came to the conclusion that his boyfriend wanted to spoon.
Dean wasn't too big a cuddler, preferring space after certain activities, but he enjoyed Castiel's arms around him so much, that he was willing to give it a go. As soon as he felt his boyfriend's arms wrapping around his waist, he tugged the man to their bedroom (he wasn't a cuddler, but he was obviously going to share a bed with his boyfriend) and onto their bed.
Cas' arms hadn't left the slightly taller man's waist, and so, when they fell onto the bed, they landed in the exact position Dean was hoping.
The ex-angel seemed to enjoy it too, going by how he tightened his arms around the hunter's waist, sighing against the back of his neck.
If Castiel wanted to get protective, every once in a while - which was what Dean assumed was going on here - then he could handle some spooning. And, in the morning, when he felt a certain piece of his boyfriend's anatomy pressed against a different piece of his own anatomy, well, who was going to complain?