See also
Dean Winchester
Castiel
Taking a Four Loves approach:
*Family love
** Dean <=> Sam
** Bobby <=> Dean and Sam
*Romantic love
** Castiel <=> Dean
** Ruby => Sam
*Friendship
** Pamela <=> Dean and Sam
** Ellen and Jo <=> Dean and Sam
*Caritas
**the Fishers => Sam and Dean
**Castiel, Anna (other angels, possibly; God, let’s hope) => humanity
All the people who love Sam, including Anna, John and Mary, give Dean the strength to save him. They love Dean just as much, and he has to believe it. But it’s Castiel who brings it all together.
Sam and Ruby: I think it’s safe to say at this point that he’s not in love with her. She might sacrifice herself for him, but he doesn’t deserve it.
Lilith doesn’t love anybody: the demon in her is too strong for her to be capable of it anymore. Which is kind of irony, if the Grail is powered by love: then she can’t switch it on.
All of the angels are capable of caritas even Uriel; even if he finds humanity a waste he can still love them in a grudging sort of way. The thing to remember is Castiel’s attitude towards humanity: they’re works of art, and loving humanity is akin to his love for God.
He loves humanity in a generalized sort of way, but loves Dean specifically, and very humanly. What began as caritas and fascination has evolved into something specific and focused, and a little terrifying for them both. But it ends with commitment: Castiel’s devotion to Dean is what saves him, and Dean’s devotion to Castiel is what gives Castiel his chance at a human life and a different sort of fulfillment.
We’re taking it as a gimme that there’s more there than just friendship: the question is, how much more and do they act on it? I kind of like the notion of Castiel being given a chance at a human life–as a probation, really–but first I need to show that he wants that, I think. If Castiel is on probation, as it were, should Dean be charged with keeping watch over him? This aspect is more Wim Wenders mythos than Kripke.
If Castiel is given a chance at life rather than killed outright that might necessitate some rearranging with the SPN view of angels–maybe those four are the totalitarian ones and even God isn’t that harsh.
Back to the theme of the redeeming power of love, Dean’s love for Sam saves him from himself, and Dean’s love for Castiel saves him from destruction. He might even be impressed with his power 
.
Further plotting:
There is longing and desire (and kissin’) throughout, but there’s no confession (and sexin’) until after Castiel rescues Dean at Medicine Wheel. Cas takes Dean to the Fishers’ home to rest and heal, and while they’re there there’s mutual “I love you”‘s.
*Except in the actual writing it didn’t go that way at all. So it goes. The story wants what it wants .
First kiss takes place near the beginning, maybe even the first scene? (More rewriting, then.) But then it’s a long time before they’re together again in anything other than dreams, and there should be lots of longing and missing and all that good stuff. Longing is very important.
A question that came to me the other night and was reinforced by fandom_secrets:
Fandom secrets
What does Castiel get from Dean? Dean seems to be the winner here: he’s got an angel who loves him no matter what. What does he love about Castiel? How is this relationship rewarding for Castiel? Hmmm.
And now, the sex question: does there need to be sex in the body of the story, or just the longing? At least until Castiel comes back in the last chapter/epilogue? Everything before then is affectionate, hugs and kisses and comforting and so on . . . or I could just write the thing and see where sex fits in later, if it does at all.
If they wait until after Castiel comes back, with a body of his own or the vessel gave him his body–assuming the vessel has died and won’t be using it anymore–that gets rid of any question of using the body inappropriately, I’d say.
I kind of like the notion of Castiel showing up in a body of his own, and then Dean knows him by his eyes or the way that he kisses. And ”then” sexin’.
It’ll up the longing factor if they don’t have sex because Castiel won’t while he’s in the vessel, an Dean won’t for the same reason. Longing is good. We like longing. And then when Castiel shows up again it’ll be like, “Oh thank God, we can fuck now.”
Dean will have to think about what he wants, too–if he loves Castiel enough to redefine himself.
Post 4.16 spoilery stuff:
Dean unlocked the first seal of the apocalypse by being “the righteous man who sheds blood in hell.” So now he’s got not only the guilt of failing his family (Sam’s turning more and more to the dark side, as evidenced by the increasing yellowness in his eyes) but the guilt of endangering the whole world. He thinks he can’t do it: he thinks it’s too big. And Sam thinks Dean isn’t strong enough, either.
Castiel seems torn: on the one hand, he doesn’t want to cause Dean any further pain (the line is something like “I would give anything not to ask you to do this” before Dean starts torturing Alastair, and that seems to be enough to change Dean’s mind), but on the other, the person who broke the first seal is also the only person who can stop the Apocalypse. If Dean doesn’t do it, no one else can. And Castiel loves the world too much to let it fall.
The big bang itself is as much a love story as it is an adventure: it’s about two people who’d do anything for each other, no matter how much it scares them, and no matter that they don’t think they’ll be together in the end. It’s that longing again. It’s sacrifice. If Dean thinks he’ll stop the Apocalypse but lose himself, or lose Sam, will he still do it? Will he do it for the world? For Castiel?
External links
Because God commanded it, Dean/Castiel ship manifesto by vichan
tracy_loo_who’s meta, particularly why Castiel is something/someone specifically for Dean
this lovely piece of fanart
All You Need Is Love by angelsdeath15