Fixten
See, this is what i meant by save it for a better time. Here you have alex already alienated and his backstory established as betrayed, so we only get bland worldbuilding leading up to a predictable outcome. If instead you skipped that and did it after the class assignment, not only does the gf have an actually valid and not absurdly shallow justification for leaving him, you also have a reason to establish the hero cast in a more positive light first, to contrast the betrayal. It's not immediately obvious the mc will be a "useless" outcast, so it's more impactful when he gets a **** class and his friends abandon him. That neatly segues into exposition on his insecurity issues and gives him even more reason to freak out, but it also doesnt have to be the only focus of the scene anymore since other stuff can be happening while he angsts. None of the things you've done are totally unacceptable, or even unusable, but the order you did them in is very bland and hard to like.
Also tbh for those saying they'll keep there hopes up remember this is isekai don't go in with expectations unless the expectation is to be let down not that I'm saying its gonna be bad but more often than not isekai end up letting people down in some aspects just altogether tho I'm gonna continue this when it gets quite a bit further in so i can binge it but for now I'm gonna leave it on the back burner . Yours truly the best the knowledgeable skeptic P.S. sure this novel has potential all novels do but i say with a heavy heart ............... Meh even for having followed such a basic cliche template there is zero emphasis on any of the characters and even for such a basic isekai scenario it came off as extremely rushed and had zero thought given to any sort of pacing and felt like it gave you less than even the most basic of prologues so from a writing the inner me is screaming (ABANDON SHIP ITS NOT WORTH THE TORTURE) but i like to be an optimist so I'll read it until the end or when the author decides to quit as i don't like doing things half way.