Not sure why people think he's a deliberate self-deprecating moron just for kicks.
I'm bored during work, so let's recap:
--His issues with his family stem from his sister causing a head injury out of jealousy, him assumedly being abducted for a week, and discovered in the next town over. This left him feeling like he was just a nuisance to his sister, and mom by extension, so from then on, he never sought their attention and his mom took it as, "wow, this kid's so independent, lucky me," and didn't realize she was neglecting him until her sister tried to take him away. They're now scrambling to maintain a relationship with him without scaring him off. The thing with the shoes plays into this, since his mom's initial reaction was to believe the teachers' account over his, which sucks, but I mean, kids will say whatever to avoid getting in trouble. It's just an unfortunate situation.
--He firmly believes that his childhood friend has been dating an upperclassman, and that she let him know ahead of his confession to avoid an awkward situation. However, she's kind of garbage, because she lets him continue believing that, even though the guy she dated for two weeks clearly went on a smear campaign after she wouldn't put out (garbage attracts garbage, I guess). By the time she finally comes clean - in a bit of an overwhelming manner - he doesn't know how to respond since his feelings for her have become distorted as hell.
--He became absorbed in basketball as a way to process and cope after supposedly being sidelined by his childhood friend, rather than being an insufferable, jealous asshat, though honestly, it's on her for never bothering to clear it up and just assuming he'd eventually piece it together and make the first move, which she already swatted away. The basketball girl who falls for him confesses, but he can't move on yet, and then doesn't get to because he suffered an injury saving her from a fall, missed the end of the season, and killed the team's morale. Doesn't help that he believes her confession was a prank, after overhearing her telling her friends she doesn't actually have feelings for him.
--Because of just how poorly his elementary teachers handled the shoe incident, and how he had to operate alone to resolve it, he grows up thinking that the only person who would ever have his back is himself. He finds himself in a mindset akin to, "No matter how I behave, I end up causing some kind of conflict, so by that logic, I'm a troublemaker by default, who doesn't deserve the benefit of the doubt." If there are any "self-deprecating moron" elements abound, it's in this point, but there are certainly reasons behind it. Mental health issues and emotional trauma don't typically stem from, "I feel like being Autistic for attention this morning."
Beyond that though, things sort of fall apart, and the story continues well past the point where it should have ended. It might as well have spun off into another series called, "The Girls Who Traumatized Me Took A Back Seat, And Now I'm Japanese Politics Jesus With Unlimited Powerful Connections and Upperclassmen Literally Offering Me Sex With Condoms in Hand."