I said this when I greenlit your tale:
My cautionary note is that this will be tempting to just write endlessly about stuff that already exists. This needs to be a story on it's own, so keep your focus narrow to this guy and what he's going through. Remember, you can always write more about this guy, not everything needs to be said all at once. If you see your word count creeping north of 3k, take a moment and reflect about whether everything needs to be said NOW, or can it wait.
You did both things I warned you against. You wrote something over 4k words AND you made it mostly about the shit he remembers. Tedious and endless memories about shit we all know. It is a slog to read, just as I anticipated it would be.
There are few SPaG errors in this, which makes it easier to read. I appreciate that you put the work in on that.
However, the bouncing back and forth between the memories really breaks up the flow in a way that makes it very difficult to keep the strain going. HE struggles with keeping it all straight and he remembers literally everything. You keep it straight because you know what you are trying to say.
But your readers are just going to get lost in the detail.
I would say that most of the memory contexts could be replaced with a single line stating that he remembered everything. Putting all the one liners in there read like you were trying to encapsulate all of the Greatest Hits of the SCP Wiki in one skip and hope that nostalgia would keep your reader interested.
But it doesn't work that way. You have to justify crosslinks in order for them to be a net positive, and this really doesn't do that in any meaningful way.
It reads like a slog down memory lane but without the enjoyment of actually reliving those memories.
This needs to be massively reduced. Focus on the meat of the story, the fact that this dude is effectively immortal and remembers everything. The memories haunt him, they shouldn't haunt us too.