"You and Me" by Nicola Rayner. This mystery thriller offers an interesting depiction of limerence (a theme I rarely read about in novels, I might add). The main character became besotted with a classmate named Charles when she attended a prestigious boarding school and even though school ended AGES AGO she can't get him out of her mind. Obsessive infatuations can really blind you to the truth of who someone is and I think that's the message the author is trying to convey here. Interesting twist at the end. Didn't see it coming at all. Too much of a slow-burner however, imo.