The author really loves to just pour salt into this kid's wounds.
Also pretty sure that's illegal and if it's been spread around the school to the point that everyone knows about it, the authorities would have gotten involved considering he is in witness protection.
Here's a rule about story telling: watching a character suffer just to suffer is not "deep" or interesting, especially when the author has worked hard to establish that they're morally in the right. Literally the fact that MC just goes through all this shit for no deeper reason than the author's sadism does not make the story enjoyable. It just makes it frustrating to read, especially when everything just so happens to be looking up for him and then everyone just instantly turns against him is just predictable and annoying.
If the author wanted it to be interesting, he/she would either have deeper themes connected to this Sisyphean struggle about how circular the events in his life become and how society rejects him, and then uses that to build him into a more interesting figure, such as having him feel like such a Pariah he becomes an egoist, or the story goes full into the absurdist route. Alternatively, if the author doesn't want to tackle philosophy, he/she would set it up so there's tension in having someone investigate the case further to uncover the truth that he doesn't want revealed as the "fall guy," and so there's this ticking clock as everything gets uncovered and he is stuck in the dilemma between letting the truth getting revealed with him being exonerated, but there being this moral tension because he doesn't want to drag anyone into his problems or expose the trauma that his loved ones face.
Also how I'd fix this chapter specifically is I think it would have been more interesting if he has PTSD from event and watching a molestation happening, so when she brings up sex, he essentially explodes at her and runs off, causing a more character-based reason she would turn on him that makes him partially culpable, but in such a way that we can't blame him directly and we can still empathize with his struggle. It's significantly better than the random 180 all his friends go through where everyone just suddenly becomes an asshole for no reason, rather than trying to maybe justify it to themselves, or try to deny it instead of instantly buying it.