The Other Side of Paradise by Lily Seabrooke

Allison promised a casual fling. Stella is anything but casual.

Allison Holt is in no place for a serious relationship or serious feelings—working summers at an island resort to help her pay her way through art school, and still reeling from her last whirlwind romance turning into a nightmare, she’s lost her spark for love. But when she promises her friend she’ll try a no-strings vacation fling, she’s not expecting the resort guest she has a crush on to be the one helping her find that vacation fling.
Stella Valerie Bell doesn’t want to be on vacation. Taken away from her summer plans by her rich family to attend a family vacation, she’s surrounded by luxury but only wants one thing: to be her own person. So when her sister gets into a fight that splits the family, she’s all too happy to break off from the family herself and join her sister’s new friends helping Allison score the summer vacation romance of a lifetime.
But seeing the way Allison looks at her when it’s just the two of them, maybe Stella isn’t so straight after all.