I need to have that written down. Even if listening to it again right now will kill me.
Here’s Cas’ speech from Episode 15×18 “Despair” (that ep is so properly named…)
Cas: When Jack was dying, I… I made a deal to save him.
Dean: You what?
Cas: The price was my life. When I experience a moment of true happiness the Empty would be summoned and it would take me forever.
Dean: Why are you telling me this now?
Cas: I always wondered ever since I took that burden, that curse, I wondered what it could be, what my true happiness could even look like. And I never found an answer, because the one thing I want is something I know I can’t have. But I think I know… I think I know now. Happiness isn’t in the having. It’s in just being. It’s in just saying it.
Dean: What are you talking about, man?
Cas: I know… I know how you see yourself, Dean. You see yourself the same way our enemies see you. You’re destructive and you’re angry and you’re broken. You’re daddy’s blunt instrument. And you think that hate and anger, that’s… that’s what drives you, that’s what you are. It’s not. And everyone who knows you sees it. Everything you have ever done, the good and the bad you have done for love. You raised your little brother for love, you fought for this whole world for love. That is who you are. You’re the most caring man on Earth. You’re the most selfless, loving human being I will ever know. You know, ever since we met, ever since I pulled you out of hell, knowing you has changed me. Because you cared – I cared. I cared about you. I cared about Sam, I cared about Jack. I cared about the whole world because of you. You changed me, Dean.
Dean: Why does this sound like a goodbye?
Cas: Because it is. I love you.
Dean: Don’t do this, Cas. [The portal to the Empty opens.] Cas!
Cas: Goodbye Dean.