What No One Knew. Dying Hearts Series, #2

Benjamin and Callie knew how to survive. They just didn't know how to stay. Before Elijah and Jolie found healing in The Ones Left Behind, there was another story. A secret friendship. A hidden love. Two broken people who promised each other thirty days of truly living instead of simply surviving. No one knew they were together. No one knew how much they meant to each other. And no one knew that losing one would destroy the other.
You already know how their story ends. Now discover how it began. TW: Both of the main characters commit suicide. This book deals heavily with this subject, as well as mental illness. The suicides take place on page.