Gravity (Wilde Boys, 1) by Sara Cate

Three months on a private island. Two men. One million dollars. All she has to do is tame Nash Wilde. Two years after Zara's sister and her boyfriend were killed in a plane crash, the last person Zara expected to show up on her doorstep was Preston's father, Alistair Wilde. Yet, there he is, with an offer Zara may not be able to pass up: be his son's girlfriend for three months, live with the two of them in a remote house, and one million dollars is hers for the taking. The challenge turns out to be harder than she ever expected. Nash isn't just wild, he's dangerous. And Alistair is far more broken than he lets the world believe. The three of them are bound by grief. Only Zara can feed Nash's hunger and heal Alistair's pain. Lines are crossed. Rules are broken. On the island, there's no one to tell them this is wrong. And now she'll have to choose before she tears their family apart. But she belongs to both of them― One of them has her body. The other has her heart.