Overly realistic writing does not make for satisfying writing.
Why?
Because in real life, people rarely if ever change or develop.Even traumatic events aren't often as lifechanging as they are depicted in stories. This applies to this manga as well. Kazuya is a character that remains stagnant and pitiful, surrounded by abusive and manipulative characters that also do not change. There are no satisfying resolutions, and the story thrives purely on drama after drama.
... Just like real life.
The thing is, the mangaka didn't make that very clear, so all the readers who now have sunk cost fallacy with this manga are endlessly coping for a happy ending that was never in the cards to begin with.