When does Olive realize that her feelings about Ethan have changed in the novel, The Unhoneymooners?

During their fake honeymoon in Maui, Ethan and Olive decide to take a boat ride off the coast. This is a critical location because they are stuck together on this boat unable to escape Sophie and her fiance, Billy. Due to the circumstances, Olive and Ethan are forced to act as though they are just married, and it is when Olive starts to realize that she may not hate Ethan nearly as much as she previously did. On the boat they go scuba diving, and it is this moment that brings their relationship closer together. Under the water and away from prying eyes, Olive sees a very different side of Ethan, one that she enjoys to be around.