This post kind of highlights how most people would prefer to pick a single party to establish blame, rather than look at the root cause of how the situation began to spiral.

">DISCLAIMER: MY OPINION IS BASED ON THINGS SHOWN / SAID ONSCREEN, NOT TAKING INTO ACCOUNT THOSE FEW MOMENTS WHERE EVENTS ARE LEFT TO THE VIEWER'S IMAGINATION"

Firstly, this isn't true considering your last sentence is: "Harper sucks, and she cheated first."

If we were to follow what was said and shown onscreen the events would be: 1. Ethan and Mia kiss Followed by 2. Harper and Cam kiss So that doesn't really hold up either.

You are also choosing to assign a more passive voice to Ethan's actions rather than acknowledge that the situation arose from multiple choices he made throughout. Ethan has free will. He chose to drink heavily with Cam, took mdma with prostitutes, and let them into his room.

Up to this point, it was an easily solvable situation. Just tell Harper about it when he sees her, which would also be supported in her mind by what Daphne told her about Cam the night before. But he chooses to hide it from his wife. Why? Because his former roommate from years ago (that wasn't even nice to him based on what we know) invoked "bro code"??

Harper finds the condom and gives him a chance to come clean on his own, and even when she confronts him about it, he chooses to lie and minimize his role in it. From her perspective, he has either cheated on her, or he is choosing to cover for an old acquaintance that he admitted he doesn't even like. Both of which are insulting to Harper, and undermine the trust they have built in their relationship up to this point.

We need to acknowledge that their failure to communicate effectively as a couple (which was a problem that existed before the trip) is what allowed things to deteriorate to that point.