The Unhoneymooners Book by Christina Lauren

Olive Torres is used to playing it safe while her identical twin sister, Ami, enjoys good luck in abundance. When Ami's wedding leads to a food poisoning disaster for the entire bridal party, the only two who escape unscathed are Olive and Ethan, the best man and Ami's brother-in-law. The twist of fate lands them on a free honeymoon in Hawaii that was meant for the newlyweds. The catch? Olive and Ethan can't stand each other. Forced to pretend they're happily married, they navigate awkward situations and unexpected attractions in this humorous and heartwarming