Blue Moon (The Immortals) by Alyson Noel

What's on the back of the book:
Some things are meant to be gone
Forever.

Things have changed for Ever since she fell in love with Damen. But just as her powers are increasing, Damen seems to be weakening. Panicked at the thought of losing him, Ever finds a path to the in-between world of Summerland, where she learns the secrets of Damen's tortured past - and accidentally discovers a way to twist time. Now she can save her family from the accident that killed them. It's all she's ever wanted - but so is Damen.
And Ever must choose between them . . .

A piece from the book:
In English, it's even worse than I anticipated. And I'm not even halfway down the aisle before I notice that Damen is now sitting by Stacia.
And I'm talking hand-holding, note-passing, whispering distance from Stacia.
While I remain alone in the back like a complete and total reject.
I press my lips together as I make my way toward my desk, listening to all of my classmates hiss:
"Spaz! Watch out, Spaz! Don't fall, Spaz!"
The same words I've been hearing since the moment I got out of my car.
And even though I've no idea what it means, I can't say I'm all that bothered by it - until Damen joins in. Because the moment he starts laughing and sneering along with the rest, all I want to do is go back. Back to my car, back home where it's safe -
But I don't. I can't. I need to stay put. Assuring myself that it's temporary - that I'll soon get to the bottom of it - that there's no possible way that I've lost Damen for good.
And somehow, this helps me get through it. Well, that, and Mr. Robins telling everyone to shush. So when the bell finally rings, and everyone's filed out, I'm almost out the door when I hear:
"Ever? Can I speak to you for a moment?"
I grip the door handle, my fingers closed and ready to twist.
"I won't keep you long."
And I take a deep breath and surrender, my fingers cranking the sound on my iPod the second I see his face.