I know I know, I’ve said this before but...
CASTIEL: Mercy, brother, please!
EFRAM: Brother? Ha! What are you?
CASTIEL: W-what? I'm an angel of the Lord.
EFRAM: That so? 'Cause, near as I can tell, when you have to choose between heaven and the Winchesters . . .
JONAH: You choose them.
EFRAM: Every time. So, see, you're not my brother. And if I had it my way, I'd take this blade, stick it in your heart . . . and call that a damn good day.
Dean: How you doing? You good? I mean, you know, the whole Lucifer thing.
Castiel: I was just... so stupid.
Dean: No, no, no. It wasn't stupid. You were right. You were right to let Lucifer ride shotgun. Me and Sam wouldn't have done that.
Castiel: Well, it didn't work.
Dean: No, but it was our best shot, and you stepped up.
Castiel: I was just trying to help.
Dean: Well, and you do help, Cas. You know, I-- You know, sometimes, me and Sam have got so much going on that.. we forget about everyone else.
Castiel: Well, you do live exciting lives.
Dean: Yeah, that's one word for it. But you're always there, you know? You're the best friend we've ever had. You're our brother, Cas. I want you to know that.
Castiel: Thank you.
It’s not like Cas hasn’t always tried his best for Heaven, for the other angels (well except that time he was suffering from Leviathan poisoning and sort of obliterated them willy-nilly, but we’re past that...). What Efram and Jonah tortured him for here, what they were willing to kill him for, what they’d disowned him for--
Dean knows all of it, knows why Cas said yes to Lucifer, even though it didn’t help in the end, but understood his reasons for putting the rest of the world at risk that way, and not only reassured him that he’d done the right thing, but that he’s still family, too. That he’s a brother, and that he’s wanted and accepted for who he is.
This still makes me all verklempt.