What I Thought Was True book by Huntley Fitzpatrick

Gwen Castle has never so badly wanted to say good-bye to her island home till now: the summer her Biggest Mistake Ever, Cassidy Somers, takes a job there as the local yard boy. He's a rich kid from across the bridge in Stony Bay, and she hails from a family of fishermen and housecleaners who keep the island's summer people happy. Gwen worries a life of cleaning houses will be her fate too, but just when it looks like she'll never escape her past—or the island—Gwen's dad gives her some shocking advice. Sparks fly and secret histories unspool as Gwen spends a gorgeous, restless summer struggling to resolve what she thought was true—about the place she lives, the people she loves, and even herself—with what really is.