Destiel is probably one of the most common OTP's in every fandom. The idea of Dean and Castiel makes thousands of children cry everyday, but the homophobia present in the writers of Supernatural prevents them from writing these two characters together. They've provided sufficient sexual tension to make it happen, and I believe that if it was a boy and a girl, it would've happened long ago, but still the writers could easily make it canon. I believe they need to build up the tension at a greater pace and then they need to let it climax in an episode called "I can't Help Falling In Love With You," Where they confess their love. After all, it wouldn't be the most far fetched storyline in the show. The Supernatural Book Series/ prophecy is far more far-fetched.