I think the fic you are looking for is "Songs of Love and Hate, or: Alas, a Cornucopia of Love" by amor_remanet.

http://bodasdesangre.livejournal.com/28270.html

Pairings: Dean/Castiel, Lisa/Becky(/Chuck), Barnes/Damien, Sam/Gabriel(/demon!Bela), Bobby/Crowley, Cupid/OMC angel.
Rating: R, overall; NC-17 for one chapter.
Word Count: ~54,000 (over thirteen chapters & an epilogue).
Warnings (if applicable): accepts 5.22 "Swan Song" as canon (spoiler free for s6), archangel!Cas, God/aspect-of-God!Chuck, language, angst, schmoop, some Gabriel-flavored crack, fade-to-black m/m hurt/comfort sex, explicit m/m rough sex (including: bondage, knifeplay, wing!kink), non-canon angel- and demonology, some meta, some meta-crack, and Cupid flitting around, making everything crazy.
Summary: Castiel is up in Heaven, miserable and making life hard for the other angels. Sam is out of Hell and can't get Crowley and Bela to stop treating him like King of the Demons. Dean is down on Earth, miserable and making life hard for everyone else — especially for Lisa and Becky, who might just be pregnant with Jesus. Gabriel and Cupid decide to stick their noses in and set everybody right. Too bad they can't make plans to save their lives.