The Secret Of Us by Zarin Madiyha

Izzy Evans thought her final year of boarding school would be a quiet countdown to freedom—a chance to dodge university brochures and steer clear of her ex, Ryan.

While everyone else seems to have their futures mapped out, Izzy is paralysed by the thought of making the wrong choice.
Noah Park just wants a fresh start. Kicked out of his old school, he’s now the new boy with a target on his back, and Ryan seems determined to make his life miserable.
But when Izzy steps in to defend him, it ignites a rumour that catches fire: Izzy and Noah are dating.
And once the school rumour mill starts turning, there’s no stopping it.

Dealing with Noah’s sudden bad reputation and Izzy’s ex who won’t leave her alone, the two strike up a fake dating deal. But the more time they spend with each other, the harder it gets to pretend that it’s not real.