As Dean stood there facing Castiel; a friend who was like a brother to him, who had saved him from hell, been there when he needed him but now all he could think of when looking at him was Charlie's lifeless body covered in blood hanging over the bathtub; Dean turned his back on his friend. "Sam and I were trying to cure you." Explained Cas as Dean turned back to face him, His face was expressionless, the light in his eyes gone. He raised his arm, gun pointed at Cas. "Maybe I don't want to be cured." Dean pulled the trigger.
Castiel looked down at his chest and saw red slowly expanded over his trench coat, he fell to his knees as he looked back up at Dean. As he looked upon his friend, his face still as cold as stone Castiel knew he was gone, the mark had taken its hold on him and there was nothing he could do to save him. Dean's fate now lies in the hands of Sam, hoping he brings Dean back before it's too late. "Dean—I don't blame you, remember this isn't really you." Castiel spoke his last words, as his back arched and his arms flung out he felt his grace go.
The blinding flash of light would always hurt his eyes, but this time he stared straight ahead at the man who had a part to play in Charlie's death, he was meant to be keeping an eye on her but he didn't and now she was dead. As the light disappeared, and Dean saw Castiel's lifeless body lying there on the ground, a pool of blood forming something gave way inside of him. The gun in his hand fell out of his grasp and hit the floor, "Cas…" whispered Dean, he fell to his knees staring into Castiel's glazed over eyes "Cas!" Yelled Dean as a single tear slid down his cheek. "No…no...Don't be dead." Chanted Dean as he stared at his friend's dead body. "Cain was right, I have to leave before I hurt Sammy."