I'm not sure specifically as there could be many different 'illusion school mate stories'. It might be about some kind of imaginary or illusory experiences involving school mates, like a daydream or a fictional account of events with school friends.
I'm not entirely sure specifically what 'School Mate Visual Novel' is about, but generally, visual novels set in a school environment often explore themes like coming - of - age, self - discovery, and the complex web of human relationships. It could feature different types of characters, like the popular kids, the nerds, the rebels, etc., and how they interact with one another. It might also touch on issues such as peer pressure, family expectations, and the pursuit of dreams while being in school.
Leaving after school to read manga isn't a good idea because it can disrupt your schedule. You might not have enough time to rest or do other necessary things like exercise. Plus, if it becomes a habit, it could impact your academic performance negatively.
I don't think you should hate it. Maybe you just haven't found what you like about it yet. Maybe give it another chance and look deeper into the story and characters.
Since I don't know the specific 'illusion school mate story', it's hard to say. But generally, it would be the school mates themselves. There could be a protagonist who experiences the illusions and his or her school mates who are part of those illusions.