Choosing books that represent “Fling” is a challenge due to the word’s definition. A “fling,” after all, is “a short period of enjoyment or wild behavior.” Many novels about sexual side stories focus instead on affairs because they last longer and often morph into difficult and tragic tales. That’s the case with the titles on this list — but each of them includes enjoyment and wild behavior, too. Any — or, better yet, several — of these will add fun and a little scorch to your vacation reading. Among them: A women bent on revenge who also has a taste for orgies, a secret affair by the sea, lovers with a connection to the real Casablanca, and a sort of Sliding Doors fantasy about love’s possibilities. 1. If you’re hooked on scandi-crime: All In by Simona Ahrnstedt You may not have thought a novel about “Sweden’s financial elite” would make its way to the top of your to-be-read pile, but look out — Ahrnstedt’s U.S. debut is smart and smoldering, using an affair between cutthroat …