The Summer of You and Me by Denise Hunter

Maggie Reynolds is finally ready for love again—until the past shows up in the form of someone who may or may not be the late husband she thought she’d lost.

Five years after her husband’s death, Maggie is finally ready to let go of him and the dreams she had for their future. A summer at Seabrook, where she and Ethan first became childhood sweethearts, seems the perfect time and place to find closure. Plus, she gets to spend time with his family, the Reynoldses, whom she loves like her own.
Unbeknownst to Maggie, her brother-in-law, Josh Reynolds, has been in love with her since they first met all those years ago. But his brother ultimately won Maggie’s heart, and Josh’s unrequited love has ruined all his relationships. If Maggie is ready to move on, then Josh is ready to lay it all on the line and come clean about his true feelings for her.
But his plans soon get put on hold when, shortly after Maggie returns to Seabrook, she runs into a man who could pass for Ethan’s twin. But he disappears into the amusement park crowd before she can confront him.