The Voice on the Radio by Caroline Cooney

This book is the third in a series, although I did not read the first two yet. Janie is still recovering mentally after discovering she was kidnapped as a young child. She loves the parents who raised her, but she's trying to accept the realization that she has another set of birth parents. Her boyfriend, Reeve, is away at college, and he's adjusting to his new life. However, he makes a big mistake. He wants to make an impression as a radio deejay, so he tells Janie's story on the air. Students and faculty at the college are drawn into his broadcasts, and they expect more. Reeve continues to share Janie's life until two things happen. Janie surprises Reeve when she visits the college, and a mysterious listener calls the station. This listener.can create even bigger problems for everyone.

You should read the first two books in the series, starting with "The Face on the Milk Carton". Reeve is an impulsive character who doesn't think about the consequences of his decisions. Meanwhile, Janie is learning to accept the fact that she has a second family that loves her, but they are all strangers to her. Obviously, it's easy to predict that she's in for a huge conflict with her boyfriend. The plot offers several different issues through Reeve, Janie, and Hannah. Be sure to read the first book in the series to learn a little bit about Hannah!