Kinda downplaying those 'experiences' in this case though. The adults don't just not listen, they vehemently insist they're right until the rest of the class turns on and bullies MC, and don't even consider that they could be wrong until he's persistent enough to prove it. The first love didn't just end poorly - she flat out lied to make him jealous/notice her when he was seconds from confessing, and didn't come clean for years, while he thought she'd been dating her senior all along. His sister didn't just say she hated him - she was jealous that he got attention she didn't and threw him off the top of a jungle gym, leaving him to bleed out with a head injury, before he was mysteriously found in the next town over like a week later.
And to what someone else commented near the top of this page: He doesn't think anyone owes him. He thinks he's a burden on everyone and overcompensates by trying to be a loner when deep down he wants genuine connections.
Comments like yours tend to be the more common sentiment though. Is it just that a lot of manga readers can't detect nuance? Or do they skim so much that they miss important context?
It's nuance when it's a focal point, not the entire story. If it was with one or two people and was a shorter story, then that would work, but it's literally everyone. After a point in time it's not a nuanced point but a point that is being hammered again and again and again.
It's like The Eminence in Shadow- the story is fantastic for so long, but after a certain point the trope tires itself out. It's like trying to build a tower of blocks putting one block on top of another on top of another- no foundational level building upwards to a peak, but a singular point thrusted to the sky intended to keep going, but it collapses in on itself because there's nothing else going on to support it.
I understand what the MC went through here, but once again, most of these things are normal kid things to experience.
-There are MANY adults (yes, even teachers) who refuse to admit their wrong to kids as they think it disrupts the power dynamics- it just gets brushed under the rug.
-Tons of people lie and don't come clean about things in a relationship or to those they like. Though let's also look at this through a more rational light- if it was true and she was dating someone else she had truly been interested in then why does the lie matter? She didn't lead him on or continue to lord it over him- it would have just became an unrequited love.
-I've never known siblings to not have jealousy over attention or things their sibling is getting that they're not and they act out. The head injury and found a town over is a bit over the top, but I'll give it to the MC in that that is truly a traumatic experience (though the head trauma thing DOES explain a lot...)
Now mind you, I don't think I have "DOGSHIT COMPREHENSION SKILLS", as is implied by the person who replied to you initially, I just happen to think that everyone has different levels of tolerance for different things, can only suspend disbelief so far, etc.