Their happy ending

Cas says goodbye

Dean -"Everybody's going to die, Cas, everybody. I can't stop it. She's gonna get through that door."

Cas - "I know."

Dean - "And then she's gonna kill you and then she's gonna kill me." He sighs with tears in his eyes. "I'm sorry." 

Cas thinks for a minute. 

Cas - "But there is...there is one thing she's afraid of, there's one thing strong enough to stop her."

Dean looks at Cas in confusion. 

Cas - "When Jack was dying I, I made a deal to save him."

Dean looks at Cas angrily. 

Dean - "You what?" 

Cas looks at Dean with tears in his eyes. 

Cas - "The price was my life. When I experienced a moment of true happiness the empty would be summoned and it would take me forever." 

Dean tries to understand what this means and finally looks at Cas again. 

Dean - "Why are you telling me this now?" 

Death (Billy) bangs on the door again, her scythe in her hand. Cas takes a minute to think of what to say. 

Cas - "I always wondered ever since I took that burden, that curse I wondered what it could be what, what my true happiness could even look like. I never found an answer, because the one thing I want." He shakes his head, tears in his eyes. "It's something I know I can't have."

Death bangs on the door again, but Dean and Cas just stare at each other, nothing else matters. 

Cas - "But I think I know, I think I know now." Cas smiles a little. "Happiness isn't in the having, it's in just being. It's in just saying it."

Dean looks at Cas, still confused. 

Dean - "What are you talking about man?"

Cas takes a step closer to Dean, holding back his tears. 

Cas - "I know, I know how you see yourself Dean."

Dean gives swallows and looks Cas up in down anxiously. 

Cas - "You see yourself the same way our enemies see you. You're destructive and you're angry and you're broken, you're your 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, see it, everything you have ever done, the good and the bad, you have done for love. You raise your little brother for love, you fought for this whole for love. That is who you are."

Death bangs again as Dean looks at the floor. 

Cas - "You are the most caring, man on Earth. You are the most selfless, loving human being... I will ever know."

Cas is still holding back tears and Dean swallows his as Death bangs on the door. 

Cas - "You know ever since we met, ever since I pulled you out of hell." A tear rolls down his face. "Knowing you has changed me, because you cared, I cared, I cared about you, I cared about Sam, I cared about Jack." He shakes his head as more tears fall. "But I cared about the whole world because of you."

Death bangs as Dean and Cas stare at each other. 

Cas - "You changed me Dean." He laughs humorlessly."

Dean - "Why does this sound like a goodbye?"

Cas - "Because it is, I love you." 

Dean - "Don't do this Cas."

There is a swishing sound. Dean turns around with his tear-filled eyes and watches as the empty crawls out of the wall. Death slams open the door, both Dean and Cas are trapped. Cas takes a step closer to Dean. 

Dean - "Cas." 

Cas - "Goodbye Dean." He takes a step closer to Dean and puts his hand on his neck. He kisses him gently on the lips. Dean's tears fall on Cas's cheeks and when Dean opens his eyes he sees Cas is smiling. Dean looks taken aback as Cas shoves him out of the way and the empty takes him, and then Death. Dean can barely catch his breath. "I love you too." He whispers to the empty room. 

Sam calls him, but he ignores it and sobs over the loss of his friend, someone he never got to love.