Heathen and Honeysuckle by Sarah A Bailey

Then:
Leo Graham knows nothing new ever happens in the small town of Pacific Shores. That is, until he runs into his new neighbor. Golden haired, honey-eyed, and sharp-tongued, Darby Andrews. The mischievous surfer is immediately smitten with the innocent girl-next-door, and vows to dedicate his summer to bringing out her wild side. As Leo and Darby's budding friendship turns into a burning love that neither of them could've expected, Leo is determined to protect it at all costs. Until he finds the girl of his teenage dreams ran away in the middle of the night without so much as a goodbye.
Now:
Darby Andrews is Crestwell, Kansas's golden child. She's always been a rule follower, save for one secret summer spent living with her grandmother in California; the consequences of which still haunt her a decade later. Darby's always done what she was told, including agreeing to marry the man hand-picked by her demanding father. While perfect on paper, Darby knows what love is, and this engagement isn't it. When the boy who's heart she broke all those years ago shows up on the cusp of her nuptials claiming to have received a letter she never meant to send him, and an offer to run away, Darby's left with a choice: remain the good girl she's always been, or become the wild spirit she's always wished to be.