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.
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.
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 228, "Justified Campaign, The Infiltration Unveiled (Part 2)", is the clearest early answer because it turns Cold Resistance Level's situation into a concrete plot event. The setup is Zhaoyang is not anything good, and neither is Great Xia, but both..., but the pressure keeps building through The Beehive's only hope for survival now is to count on the two sides....
Chapter 117, "Teng Jiao Saliva and Poison Source [Combined Chapters]", is the clearest early answer because it turns Shi Ping's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Although Xia Hong understood this principle, he had no way to improve... and follows through with To be personally commended by the leader, you three are quite lucky."....
Chapter 152, "Mirror Immortal's Killing Intent, Who Has Fallen?", is the clearest early answer because the violence around Xia Hong becomes final instead of hypothetical. The chapter gives readers a real answer by opening on At the same time, behind Yuwen Hu, two to three hundred people... and ending on As long as Brother Xia Hong is willing to lead Great Xia to join, our....
Chapter 136, "He Yuanhun, Yuwen Hu, Yuwen Dao (Three in One)", is the clearest early answer because it turns Demon Sheep's situation into a concrete plot event. The setup is Yuwen Dao, along with the nine behind him, looked at the iron arrow..., but the pressure keeps building through From such a distance, to pierce the ground so deeply, the archer's....
Chapter 150, "Green Bamboo Fence and Marking Stone, Expanding Territory", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. Early on, In the past five days, the leader has used nearly six hundred pounds.... By the end, But it was indeed unexpected for him that the Mirror Immortal Camp....
Chapter 156, "Mirror Immortal, 10 Days to Gather Beast Blood", is the clearest early answer because it turns Cold Beasts's situation into a concrete plot event. Early on, Do you think the leader's decision was meant to exclude us?" "What.... By the end, As the Teng Jiao fell, Xia Hong, without a moment's hesitation,....
Chapter 167, "Seizing the Mirror, He Yuanhun's Confidence", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The setup is Xia Hong, thank you!" A gentle voice suddenly emerged from beneath..., but the pressure keeps building through Following the voice was a black sword edge moving at incredible speed..
Chapter 151, "Pioneering, The Growth of Xia Chuan [sorry, late]", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The Logging Realm and Earth-digging Realm were essentially built up... and follows through with Why last night, Xia Hong made the decision to expand with such....
Chapter 202, "Worthless Rabble, Four Camps Bow Down (Part 3)", is the clearest early answer because it turns Xiang Liang's situation into a concrete plot event. The chapter gives readers a real answer by opening on Tomorrow night I can finally go back, I've been staying at Wuyuan for... and ending on After the stern shouts subsided, a disheveled person, hands bound,....
Chapter 194, "A Tragic Scene, Ice Skin Jade Bone, Xia Hong's True Strength", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The chapter turns that into something concrete by moving from The people who had just scattered and fled didn't get far before... to On Xia Hong's side, he began his assault..