Cas could have cried with relief when he spotted the Impala through the trees. He tried to walk faster, but his legs buckled underneath him. Cas saw black creeping in at the edges of his vision and clenched his fists in fright. Was he dying? Had he pushed his body too much? He thought that it would be ironic, and just like him, to fail when he was so near to what he wanted.

….

Cas opened his eyes slowly and was greeted with Kevin's worried face. "What happened?"

Kevin breathed a sigh of relief. "I found you unconscious outside. You slept all day and night. What happened to you?"

"Is that all it was? I was worried I had pushed myself too far and somehow caused my own death."

"You passed out from exhaustion." Kevin looked unamused.

Slowly sitting up, Cas winced as a sharp pain shot through his skull. "Where is Dean?"

Kevin's face fell and Cas felt his heart drop. "He's not...?"

"What? No! No, Dean's fine. It's Sam."

Cas was experiencing a wave of different emotions: worry, relief, confusion. They were all so much stronger than when he'd been an angel. With a groan of pain, Cas stood up and stumbled his way to the door.

He walked slowly down to the living room, and stood in the doorway. Dean was sat next to Sam, a broken expression on his face.

"Hello Dean."

Dean jumped, and gazed up at Cas in wonder. "I thought you…"

"Fell?" Cas sat next to Dean. "I did. In a fashion."

Dean quirked an eyebrow, knowing that Cas wasn't telling him everything.

Cas sighed. "Dean, I'm sorry. I…I failed."

"Cas, what are you talking about?"

Tears were falling down Cas' cheeks again. "I tried so hard to do something right. I tried to make it better. I thought closing Heaven would do that, then I could stay here at peace. But I failed you again."

Dean's eyes widened. "Me? Failed me? Cas, we've had some rough spots, but why in the hell would you think that you'd failed me?"

"Because I have!" Cas insisted. " I tried to atone for what I'd done before, but I failed."

Cas looked at Dean and realised something new. Something that took his breath away in horror and made him tremble.

"Dean, no…"

"Cas, what is it? Jesus, Cas, what's wrong?!"

Cas burst into heart-wrenching sobs and collapsed into Dean's arms.

"I can't see you. I can't see you!"

Dean's hands were patting Cas' back awkwardly. "Cas, you can see me. You looked at me, you spoke to me."

Shaking his head, Cas buried his face into Dean's shoulder. "I can't see you!"

"Cas, what are you talking about?"

Cas raised his head to look into Dean's eyes. They were the same green as always, but there was something missing. Something Dean had always had, that Cas had always seen. Now it was gone.

"Dean, I can't see your soul anymore."