{End of "The Dark Side of the Moon"}
Castiel found himself on the side of a desolate highway. He hadn't really cared where he ended up. The news that God had deserted him, deserted humanity, was too much. He needed to be alone. So, he wandered, in the dark night, down the indiscriminant road, not caring where it led.
After a ways, lights were visible in the distance. When Castiel got closer, he could tell it was a little strip mall with a few stores, and a liquor store.
"Why not?" Castiel thought to himself, "Dean seems to like this stuff." Cas walked into the store and looked around the empty store for a little while before finding the store clerk.
"Hello. I would like to purchase some alcohol." Castiel said to the bored looking man standing behind the counter. The clerk looked at him quizzically.
"Excuse me?" The clerk said, looking at Cas with a confused look on his face.
"Alcohol. I believe that it is sold in liquor stores." Castiel replied.
"Yeah, we've got it here." the clerk said, gesturing to the rows of bottles. "What kind do you want?"
"I'll take whatever is the strongest." Castiel said as he glanced around the deserted store. The man made multiple suggestions of different hard liquors. Cas thought about it, unsure of what would be best.
"I will take all of them." Castiel said. The clerk looked surprised, but went on to ring up the purchase and bag up the various drinks. Castiel left the store with two bags filled with alcohol and proceeded to sit on the curb outside the store and drink. After downing a whole bottle, Cas hears his phone ringing. Sam was calling.
"What's the point of answering anyway? What is the point of anything? God has deserted us. And I have no interest in speaking to him at the moment." Cas said to himself, beginning to feel the effects of the bottle of gin he had just downed. But, he kept drinking.
After taking a few swigs from the next bottle, Castiel stood up and stumbled away content to walk and drink until he felt better. He kept at this for days, drinking and wandering, stopping to get hamburgers when he felt like it and ignoring the missed calls from Sam and Dean.
In his drunken stupor, Castiel ruminated on the pointlessness of his situation, until it became too much for him. At least with Sam and Dean he had been doing something, even if it hadn't solved the problem, it was doing something. So, Cas checked his voicemail, noting how long Sam's message was and how irksome he found his voice, before transporting himself to the hotel where Sam and Dean were staying.
{Middle of 99 "Problems"}
