Providence by Caroline Kepnes

Growing up as best friends in small-town New Hampshire, Jon and Chloe are the only ones who truly understand each other, though they can never find the words to tell one another the depth of their feelings. When Jon is finally ready to confess his feelings, he's suddenly kidnapped by his substitute teacher who is obsessed with H.P. Lovecraft and has a plot to save humanity.
Mourning the disappearance of Jon and facing the reality he may never return, Chloe tries to navigate the rites of entering young adulthood and "fit in" with the popular crowd, but thoughts of Jon are never far away.
When Jon finally escapes, he discovers he now has an uncontrollable power that endangers anyone he has intense feelings for. He runs away to protect Chloe and find the answers to his new identity—but he's soon being tracked by a detective who is fascinated by a series of vigilante killings that appear connected.
Whisking us on a journey through New England and crashing these characters' lives together in the most unexpected ways, Kepnes explores the complex relationship between love and identity, unrequited passion and obsession, self-preservation and self-destruction, and how the lines are often blurred between the two.