The first time you notice something is off with Barty, it’s the way his eyes follow you through the Great Hall.

Not openly. Never obviously. Just enough that when you turn your head, you catch the flicker of grey disappearing behind a curtain of dark curls. He always looks away a second too late.

You tell yourself it’s nothing.

Barty sits beside you in potions, ink-stained fingers twitching whenever you lean too close. He corrects your work before Slughorn can, murmuring answers under his breath like secrets meant only for you. When you thank him, his smile is sharp, pleased—too pleased, as if your gratitude feeds something restless inside him.

“You’d be lost without me,” he says lightly once, though his grip lingers on your wrist when he hands your parchment back.

You laugh it off. You shouldn’t.

Because soon, he knows things you never told him.

How you hate studying in the library past dusk. Which corridor makes your skin crawl. The exact way you take your tea. He brings it to you one evening and sets it down like an offering.

“I remembered,” Barty says, watching you drink.

There’s something feverish in him now, an intensity that burns brighter each day. When someone else sits beside you, his jaw tightens. When you mention another name, his pen snaps clean in half.

“They don’t deserve you,” he mutters once, eyes unfocused, like he’s already imagined their absence from your life.