How does Olive and Ethan's relationship change over the course of the book in the novel, The Unhoneymooners?

Ethan and Olive begin as enemies, and Olive consistently voices her dislike of Ethan's character. The level of hate that Olive has for Ethan is to the point where she even considers giving up her sister’s free honeymoon because the idea of spending that much time alone with Ethan sounds more miserable than staying home with her sick family. In fact, it is her anger at Ethan that actually causes her to go on the trip as she doesn’t want him to enjoy the vacation alone.

Once they go on their trip, the two begin to see each other from a new perspective and learn more about each other. As they are forced to spend time together, Olive can’t help but realize how much she and Ethan have in common and she reevaluates her initial impression.

The more that Olive learns about Ethan, the more she begins to enjoy his company and realize she misjudged his personality from the start. Her growing self awareness helps her to see how she had created their initial hate for each other which could have been avoided. This causes Olive to step back and develop a new appreciation for the person that Ethan is, beyond any of her preconceived notions. By the end of the trip the two are in a full on relationship and decide they want to continue this when they return back home, underscoring the full transition from enemies to lovers.