What IF Stanley was the only person real all along, and the Narrator was just a voice in his head, this is my interpretation of this Au.
Stanley was a lonely man who worked at an office building, he will always work as he has nothing to do back at home, there was no one waiting for him after all, although he hated how boring and repetitive his job was, he had no other choice but to work either way.
So as a way to cope with his loneliness, he took the suggestion of his co-worker, Mariella, to try reading books as it might help him, he tried her suggestion and quickly became obsessed with reading, for the first in his life, he felt happy, so he spend all his free time and day offs to read more stories, there was a concept that go him hooked, the idea of a protagonist being self aware.
Stanley began to have so many ideas that he decided he should write a story, he thought of what the Story should be about, maybe it should be about him? That seems like a good idea, so he started working on his book. He will call it The Stanley Parable, when he continued writing his story, he couldn't help but feel like he isn't exactly the one writing the story, he felt that he was the protagonist, but who was the Narrator? He couldn't help but ask, no one had answered him.
Stanley wrote his story for a very long time, making sure that every plot hole will be fixed, although he is still unsure if he actually fixed all of them.
When he wrote the story, he couldn't help but feel attached to the character he created, Narrator, he didn't know how or why but the way his Character interacted as if he was real, Stanley couldn't help but fall in love with him, the Narrator would always try his best to defy his protagonist, and everytime the Narrator would make funny remarks about his character, Stanley couldn't help but laugh at it. It really felt as if he was a real person, with his own thoughts and personality.
Stanley would be honest that he felt really guilty about the other...endings, especially the Zen Ending and...the Skip Button Ending, in order not to feel so bad about it, he made sure his own protagonist will suffer as well, even though it's technically Stanley himself, he still did it, a pay back for what he did to his character.
After he finished writing the book, Stanley published it to the public, so many people loved his book, and soon Stanley became a well known Writer, they were impressed Stanley was able to write such a masterpiece even though he worked a full time job, it took serious dedication to do that, The Stanley Parable was a success! Hell even a game studio wanted to create a game from Stanley's book, that's how The Stanley Parable became a video game.
Stanley's popularity sky rocketed when the game was released, he had gained so much money and fame, even appearing on T.V, Stanley got everything he wanted except for one thing...the character he so much wished to be real, the character he created that went through the struggle for his protagonist, the only fictional person who knew Stanley's pain, The Narrator, Stanley knew that he was so attached to his Narrator, but he knows that his character will never be real no matter how much he wished or begged, he wasn't real in the first place, he was just a character Stanley created in his head, but for Stanley, the Narrator was real in his heart.
