Maybe in Another Life by Taylor Jenkins Reid

A breathtaking new novel about a young woman whose fate hinges on the choice she makes after bumping into an old flame; in alternating chapters, we see two possible scenarios unfold—with stunningly different results. At the age of twenty-nine, Hannah Martin still has no idea what she wants to do with her life. She has lived in six different cities and held countless meaningless jobs since graduating college. On the heels of leaving yet another city, Hannah moves back to her hometown of Los Angeles and takes up residence in her best friend Gabby’s guestroom. Shortly after getting back to town, Hannah goes out to a bar one night with Gabby and meets up with her high school boyfriend, Ethan.