Castiel raised the sword to his neck.
He destroyed everything he had going for him: friends, family, and a place to call home. He ruined every relationship and burned every bridge. The sword was sharp; he made sure. He wanted a quick and painless death, although he knew he didn't deserve one.
The Winchesters haven't called for him since the day he left them with the ultimatum of worship or death. He doesn't blame them. Sure, humans are flawed, but angels are nowhere close to perfection. He was stupid to believe that souls were the only way to reach enlightenment, to be respected. A god is patient, kind, and forgiving. Opposed to the qualities of the Divine, Castiel was only comprised of hate, fear, and regret.
After all the wrong he committed, he decided that this was the only possible way to right them. Unlike humans, there was no one to watch over his shoulder and tell him which paths to pursue, no one to answer his calls for help, and no one to give him a sign.
Humans had Heaven, so what would lie in store for the death of an angel? Is there even a life after death for him? He wished he knew the answers but there was no one to consult with in the dark, abandoned warehouse of which he kneeled in, the sword still glued to his hands. His knuckles were white and his hands were trembling.
This was the first time Castiel cried.
Tear after tear rolled down his checks as he knelt soundlessly on the floor.
He opened his hands and released the sword from his grip. It fell to the ground with a loud crash. With the sleeve of his coat, he wiped the tears from his eyes. This wasn't the way to right his wrongs. He picked up the sword again and pulled himself off the floor.
He transported himself to the dungeon where he and Crowley once teamed up together. He looked towards the wall at Crowley and Raphael's failed attempt to open the gates to Purgatory and realized his new plan. He walked over to the operating table that held the jar of the real blood that was the key to the ritual. Castiel opened the jar and re-drew the sigil on the wall opposite to the fake one. When the sigil was complete, his took a moment to straighten his coat and fix his tie in the way that Dean used to do for him once upon a time. He cleared his throat and began the chant.
After a moment, the wall began to break away and the gate to Purgatory was open once again. With the sword in his hand, he assured himself that what he was about to do was the right thing. He removed his coat and unbuttoned his shirt. Once again his raised the sword, but this time he pointed it towards his stomach. He closed his eyes as a final tear escaped him.
Standing in front of the portal, he plunged the sword through his abdomen and twisted the blade to make sure he tore through every inch of himself. Blood rolled down from his mouth and he opened his eyes to the most beautiful sight. One after the other, a blue aura would escape the cavity and into the portal to purgatory. As each soul left his body he could feel his energy draining at a considerable rate. It would only take a few more minutes until all the souls would have left his body and he thought of the Winchesters once again. He would never have said goodbye. His engery was reduced so much that he could barely stand. His knees were shaking and his vision was failing. Everything seemed to blur together into a dreary, sad excuse for time spent on Earth. He removed the blade from his stomach and let it fall to his feet leaving a blood-splattered mess.
The final soul left his body and the portal began to collapse on itself. It was done. He did the right thing. He did the right thing and Dean wasn't there to see it. Dean wasn't there to joke about the look Castiel had on his face and he wasn't there to wipe away the blood from the corner of his mouth. A bright, white light began to emit from where Castiel stabbed himself with the sword. After destroying the world and his friendship with Dean, which Castiel thought of as the same thing, his time was finally up.
Castiel finally turned the free will that Dean told him about to good use. When he released the souls into Purgatory, he knew that by returning them to their rightful place that Dean would have been proud of him after the months of shame he longed to erase.
Bathing in the light, Castiel's lifeless body crumpled to the floor, freed of the souls. His face was serene and the only sign of pain in his face was a tear that pooled in the corner of his eye. With a final flash, the room went dark and the wingspan of the angel imprinted itself on the hard concrete floors.