Pythagorean Love Theorem

Kosai had braced himself for high school to be new. New building, new uniform, new faces, new rules to quietly figure out. A building full of strangers who all, apparently, had somewhere to be after school and someone to be there with. What he did not expect was for the oldest, most familiar thing in his life — Saine, his childhood friend, the girl he'd never once had to consider — to suddenly become the thing he couldn't stop thinking about. And what he was the least prepared for in the end was the day she'd grab his sleeve after class, eyes shining, and tell him she'd fallen in love.With their math teacher.