The Immortals: Blue Moon - Alyson Noel

Things have changed for Ever since she met her beloved Damen - not least because she's got a whole new set of powers, courtesy of her new Immortal status. Just as she's getting stronger, though, Damen seems to be weakening. Panicked at the thought of losing him, Ever finds a path to the in-between world known as Summerland, where she learns the secrets of Damen's tortured past. But in searching for a cure for him, Ever accidentally discovers a way to twist time so 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...