Romancing the Rival by Kris Fletcher

In the small town of Calypso Falls, New York, one strait-laced woman is about to learn how to let loose–with the help of the last man she expects.
Oldest Elias sister Bree has always been the pragmatic one, putting academics and family responsibilities before fun. Now in the final year of her doctoral program, she’s this close to achieving everything that she’s worked so hard for. There’s only one thing standing in her way—and his name is Spencer James.
Spencer knows that Bree isn’t happy they’re working on the same committee. Back in high school, the pair were enemies, the hardworking Bree angry that Spencer always coasted to the top based on his family’s legacy. But now, Spencer is trying to stand on his own two feet for the first time. It would be easier to focus if Bree wasn’t so distracting–and as time goes on, he can tell that Bree is feeling the same problematic attraction.
Just when a truce between Spencer and Bree seems possible, the secret history between their two families comes to light, threatening not only Bree’s career, but their budding romance.