Otōto ni kanojo o netora retara, bijin'na osananajimi to kekkon-dōzen no dōsei seikatsu ga hajimarimashita (Associated Names)

From being cuckolded to a major turnaround! A sweet and affectionate cohabitation life with a devoted and beautiful childhood friend! Hayato Matsui, the protagonist, had his girlfriend, whom he had been dating since high school, stolen by his younger brother. On top of that, he is almost completely estranged from his family, who constantly side…