The first romance I ever remember reading with a cheating heroine/hero was Jane Eyre. While plain, oh-so-shy Jane was falling in love with Rochester, he was hiding a deep, dark secret in the attic. His wife. Many readers are able to overlook the fact that Rochester was a cheater, and almost bigamist, but I just couldn’t stop thinking about how unfair this situation was to his wife. After all, we only know his side of it. Rochester said she was crazy, but perhaps she was just mad because she was imprisoned while her husband went after a younger woman. And in the end, Jane and Rochester get their happily ever after and Bertha gets killed in a fire.
When I later transitioned to reading modern romance novels, I realized that a cheating hero was pretty much par for the course, especially for books set in the Regency when many men kept mistresses. Readers see it again and again in books like Private Arrangements by Sherry Thomas, The Marriage Bed by Laura Lee Guhrke, Your Wicked Ways by Eloisa James, Prince of Dreams by Lisa Kleypas, and many, many others.