A Room Of One's Own by NorthernSparrow
https://archiveofourown.org/works/1417834?view_full_work=true#main
Dean/Castiel

Excellent story with an interesting view on how Dean and Castiel go from friends to lovers with Dean in denial most of the way. Castiel’s interest in learning how to behave in a more human fashion in order to please Dean after walking in on him masturbating is funny as hell. It all turns on Dean finally having a room of his own and some privacy and goes downhill from there depending on your view. The wing scene is erotic the first time and hot as hell the second time. However there is a surprising depth to Dean that shows when he finally confronts Castiel on just what is happening. Dean is determined to fix what he didn’t realize was broken. He also finally realizes just how important Castiel is to him and tries to give back some of that support and devotion. The dialogue between them as they argue about fetishes and just what is a turn on is hilarious especially since Dean is trying to hide all this from Sam. The funny part is Sam who is aware of what is happening and has just been waiting for Dean to say something. He has has even nudged things along a little.