I'm not sure if there is truly 'good' fanfiction in this regard as it goes against the general positive relationship depicted in the main story. Fanfiction often contains a wide range of interpretations, but this particular theme might not be in line with what most fans expect from the Pepper - Tony relationship.
There might be some out there, but it's not a very common or popular take on their relationship. Most fanfiction tends to focus on their love and partnership rather than such a negative concept like cheating. You could try searching on some major fanfiction platforms, but don't be too surprised if you find very few or no well - received ones with this plot.
Well, the idea of Pepper cheating on Tony in fanfiction is quite unorthodox. It would be a departure from the typical portrayal of their relationship in the official Marvel universe. While fanfiction allows for creative liberties, this is a rather controversial topic. Some writers might explore it to add drama, but it's likely to be met with mixed reactions from the fan community.
Chapter 214, "Meritorious Deed, A Fortunate Accident (Part 2)", is the clearest early answer because it turns Hong Yu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Bring him over here!" "Hong Yu isn't here. and ending on In his nimble maneuvers, he not only dodged countless slashes but....
Chapter 241, "Message, Rebellion, and the Strange Wu Xiong (4)", is the clearest early answer because it turns Zhu Yuan's situation into a concrete plot event. The setup is You have mistaken the mercy of the Great Xia for weakness!" "If you..., but the pressure keeps building through The strongest in the room were merely of the Logging Realm, how could....
Chapter 160, "Night Has Fallen, The Time Has Come", is the clearest early answer because it turns Xia Chuan's situation into a concrete plot event. Early on, The pressure on the more than a hundred people holding the front door.... By the end, More than an hour had passed since nightfall..
Chapter 275, "The Stunning Sword Puppet, Vindication, Cloud Dragon Army (Part 3)", is the clearest early answer because it turns Hong Guang's situation into a concrete plot event. The chapter gives readers a real answer by opening on Although this strike was powerful, Xia Chuan knew deep down that it... and ending on With his waist split open, Xia Chuan's body was blasted away like a....
Chapter 230, "Next Step, Surrender, Set Out for Yang Lu", is the clearest early answer because it turns Yuan Cheng's situation into a concrete plot event. The setup is What are your thoughts on the next steps?" Xia Chuan sat at the head..., but the pressure keeps building through The seven heard his voice, and their excitement abated slightly,....
Chapter 243, "Hanqiong's Great Battle, Realization After the Fact (Part 3)", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with Although the situation of the guards at the gate was unclear just... and follows through with is me?" Xia Hong, realizing the situation belatedly, his complexion....
Chapter 200, "Xu An, Ten Thousand Urgent, Presenting Treasure (Part 3)", is the clearest early answer because Frost Electric Ape gets a payoff that changes the stakes. The setup is The camps refusing to merge are mostly controlled by a handful of..., but the pressure keeps building through They incite others to resist the Great Xia and even go as far as to....
Chapter 252, "A Thousand Gold for a Steed’s Bones, Yang Li Surrenders", is the clearest early answer because it turns Li Hu's situation into a concrete plot event. The chapter turns that into something concrete by moving from But as soon as the first bite of Cold Beast Meat entered his mouth,... to Zhu Rou's father Zhu Xing is Cold Resistance Level..
Chapter 189, "The Provoked Xiao Hen, New House, Xia Li", is the clearest early answer because it turns Cloud Jiao Team's situation into a concrete plot event. The chapter gives readers a real answer by opening on The First Year of the Great Xia, Fifth day of the fifth month "A new... and ending on Especially in recent days, with father and Uncle Yuan spending....
Chapter 231, "Investigating Yang Lu by Day—Whose Side Are We On?", is the clearest early answer because it turns Chen Yingba's situation into a concrete plot event. It opens with Wushuang and Hanqiong each have three Cold Resistance Levels. and closes on Wu Xiong, Wu Ying, Han Jiuli, Wu Lin, it's those four!" The....