In first-person POV, it's challenging to convey who's speaking without a clunky or clichéd paragraph of self-description.
Adding or subtracting a character in the middle of creating a lengthy work is nearly as challenging as breaking up with a longtime life-entangled partner.
We're swimming in the narrative conceit that what makes extraordinary characters interesting is their extraordinariness and what makes protagonists interesting is that they're protagonists.
Lots of things happen that characters don't know about, or only hear about. That's part of life, and is perfectly fine to include in fiction. Instead of trying to fix it, have your characters react to it.
Today is the fifth Tuesday of the month, which means that my answer to this heartfelt letter is available exclusively to my Patreon patrons.
Let go of any inclination you have to identify with your work and interpret critiques of your work as critiques of you. Critiques of your work are critiques of your work. Your job is to use them to make your future work better.
You ask for the bones of plot, but it sounds like you already have those: start, middle, end, some drama. What you need are the muscles and tendons of plot, the pull and thrust and tension that turns a skeleton into something that moves and breathes.
Take this significant aspect of your work and see it as a selling point rather than a drawback. Find venues and audiences that appreciate your work for what it is, and keep making the art that you want to make instead of jamming yourself uncomfortably into another mold.
I love semicolons; they're great. The issue is what you're doing with language and content that leads to the use of so many of them.
Nothing gets in your way more than a creative writing degree and a lot of practice doing other kinds of writing, both of which fill your head with all sorts of ideas about what writing should be like.