Glimmer by Phoebe Kitanidis

When Marshall King and Elyse Alton suddenly wake up tangled in each other's arms, with no memory of how they got there or even who they are, it's the start of a wild supernatural ride. A bizarre and creepy roller coaster of magic and memory, twisting and plummeting through their separate pasts and shared future. Will the mysteries they're trying to uncover restore their memories, or spell death to the "perfect" town of Summer Falls...and to their own budding romance?