For me cheating in a story, it shouldn't be obvious. Looking at a decision, i don't want to look at the choice and know this is going to lead to this or that. I like nuance and ambiguity. And for an adult story/game that isn't what is necessarily needed or wanted or is just difficult to achieve that.
One of my favorite games on the site a kinetic story with no choices and is about a wife cheating on her husband. Before i download it and play it, i know this is what i'm getting.
For this story right now, thinking about it, i would write the cheating aspect with one of the male antagonists finding the the wife's phone on the coffee table. Looking at the photos she has been sharing with her husband. Angling a cheating opportunity like that. Steering right away from the tropes usually associated with NTR stories.