|You do a great job of creating a mood. Simon has clearly moved beyond depression and despair to meaninglessness, or nihilism. You do an excellent job of maintaining a consistent voice in what is really a journry through the mind of your main character. I note a few instances where I believe slight changes might be helpful.
First, "He walks through the hallways of the dim building..." I might write as "he walks through the dim hallways..." This gets rid of bthe use of the word "building" in two consecutive sentences, and you already have him in the building in the first sentence, so we know where the hallways are. I love the second part of that sentence about the crowd of emotions and thoughts surrounding him.
Second, in the sentence beginning "An acquaintance of his..." I would omit "of his" and just say "an acquaintance"
Third, I think the sentence that begins "He knows that he is just one insignificant amalgamation of cells..." works great. It shows that while Simon may be thinking about nothing and everything, he is doing so on a sophisticated level.
Fourth, in the sentence that begins "Still, none of these controversial activities..." I think I would omit "controversial." Since you have described the specific activities in the previous sentence, I think the reader can assume they are controversial.
Fifth, in the last part of that same sentence reading "any facade of meaningfulness to reality: I think I would omit "to reality."
Sixth, I think your imagery is great in the sentence reading "...the mass of human life clogging the hallways that are the arteries of the school"
Seventh, the sentence ending "only to most likely be faced with the same problems about the pointlessness of existence that he is currently being faced with" I might try to simplify by writing "only to face the same pointless existence as himself."
Eighth, I love the sentence that begins "they chatter about things he doesn't care about..." with its three-time use of that 'Doesn't care about' phrase.
In conclusion, I found the story interesting and likeable, even though it could be depressing. I like the way you end the story, with Simon cocking the pistol, but leaving it to thr reader to think about whether he fired it.
Thanks for the read, and keep on writing.