Stalker x stalker is the closest to what you're looking for, though they're not in school there are some school flashbacks
Red mansion (not school life, smut is there, but also obsession)
derail (it's school life but there's smut, closest i got to fitting the bill uh)
Moritat (no smut, not school but highest level codependency mindbreak shit tho one of my favs, kinda underrated)
The Prefect's private garden (one sided yandere but their counterpart has a spine trust, school life, smut, psychological)
Heavy boyfriend (one-shot)
The edge of ambiguity
Wrong recommendation here
https://www.mangago.zone/read-manga/heavy_boyfriend/
https://www.mangago.zone/read-manga/osananajimi_irony/
Hey pookies give me your best yandere x yandere BL plss preferably school life (it doesn’t have to be) and no smut just BL (if you can’t help it then smut is ok). I just wanna feel obsession rn