A brief look into how Castiel has changed over the course of Supernatural, shown through introspection and "what if" (AU) scenes. MAJOR SPOILERS for seasons 4-11
Sequel to "Too Far Gone" (and probably won't make sense without reading that first) THAT Summary: All at once, Sam's wall cracks, crumbles, then collapses altogether, and he's trapped in a place he doesn't know how to get out of. Basically... That story ended depressingly and this is a fix-it of sorts
Sam and Dean's relationship is still rocky at best, and just when Sam thinks he has control of things...he doesn't. Short and not-so-sweet one-shot set sometime in early season 7 when Sam's losing his mind (literally).
All at once, Sam's wall cracks, crumbles, then collapses altogether, and he's trapped in a place he doesn't know how to get out of. One-shot with possible follow-up.
When the Doctor begins to mourn the fact that he's harmed or pushed away nearly everyone who ever cared about him, he realizes that there actually is someone for him to go to. Someone who understands and accepts him for what he's done and who he really is.