It's Not Summer Without You by Jenny Han

When something is perfect, you hope it never ends.
Belly's long hot summers at the Fisher boys' beach house are over.
Conrad, the only boy she's ever loved, has left for college, taking her heart with him.
And Jeremiah, his younger brother, is still Belly's best friend - but maybe friendship isn't enough for him anymore.
But when Jeremiah calls and says that Conrad has disappeared, all roads seem to lead back to the summer house.
Will Belly spend another summer chasing after Conrad, or will she finally let him go?