Lua Nova by Stephenie Meyer

After a traumatic incident, a young woman is left devastated when the vampire she loves abruptly leaves to protect her, plunging her into grief and reckless behavior. She forms a close bond with a childhood friend who offers comfort and reveals a hidden werewolf community, escalating tensions between supernatural groups. Misunderstandings and despair drive a dangerous chain of events that culminates in a desperate effort to undo a fatal mistake and confront powerful, vengeful forces.