The Boy I Hate by Taylor Sullivan

Samantha Smiles and Renee Montgomery have been best friends for over a decade. They’ve shared laughs, secrets, and a mutual hatred for one person: Tristan Montgomery, Renee’s older brother. He was the guy every girl wanted, and every guy wanted to be, and it wasn’t uncommon they’d befriend his little sister just to get closer to him. Which was exactly how Samantha became Renee’s saving grace. She was the only girl Renee could trust not to fall in love with her older brother.
Until the one night Samantha spent with him alone, leaving her questioning everything she’d ever known about the blond headed heart-throb.

Years later, Renee asks Samantha to be her maid of honor. With no other option, Samantha is forced to drive cross-country with the focus of their teenage ire.
He was her first kiss.
Her only secret.

Can Samantha survive the trip cross-country with the reckless Tristan Montgomery? The guy who did what he wanted, whenever he wanted, without worry for tomorrow? Or will she discover a different side of him. One that’s sweet, funny, and maybe a little bit vulnerable. And fall completely and helplessly in love for the first time in her adult life with the one man who could cause her to lose her best friend forever?