The description of this question was very similar to the plot of a common novel. It might involve some ethical and emotional issues. However, according to my knowledge of online novels, an ex-girlfriend scheming the male protagonist's fiancée sleeping with his brother is usually a complicated fantasy novel or martial arts novel. It might be similar to the plot of a novel like " Fight Through the Sky " or " Sword Comes." This type of novel usually involved magic, xianxia, or fantasy elements. It was a story about the protagonist who eventually became a powerful existence through a series of challenges and adventures.