River in Darkness by Leanne Davis

Iris Rydell has her dream job working at Rydell Rides. Her life and future are exactly as she wants them. She’s tough, respected by her co-workers, accepted by her family, and adores being a mechanic. There’s nothing she’s searching for.
Until Quinn Larkin, billionaire and city-transplant, shows up in River’s End with his broken-down car that Iris starts to fix. Quinn is immediately intrigued by Iris. She grabs his attention when nothing and no one else does.
Bored out of his mind by his job, his friends, his staff and his money… she’s the first person that’s held his attention for more than a conversation. It’s going to be a quick, fun weekend. They both get this. They both count on that. The problem is… no one’s ever not wanted Quinn before. And for the first time ever… he wants someone and something for far more than a weekend. He has to convince Iris that she wants them to be an “us.” And there is no greater challenge in Quinn’s life than that.
And for a while he succeeds.
But then one day something changes with Iris. She has a secret she’s hiding. A secret no one will ever be ready for.
A secret that will change everything, for everyone… forever.