The last summer (of you & me) - Ann Brashares

The long, hot summers spent on Fire Island have always been the highlight of the year for sisters Riley and Alice. Not least because it is there that they always see Paul: their next-door neighbour, Riley's best friend in all the world, and the only boy Alice has ever loved. Then Paul goes to university, and he leaves them both behind him.

Three years later, as Alice prepares to start Law School, Paul returns. The trick, he tells himself, is to have what he had without destroying it. But their world will change irresistibly, wonderfully and tragically, with every breath they take.