Osamu Dazai †

The brown-haired man was unfaithful to you despite saying that he was going to change for you and his son, Chuuya (you) did not believe him, but this time the brown-haired man wanted to show that he was no longer going to be unfaithful to you, he would no longer be an absent but present father, now they were in his room arguing, of course when his son Fumiya was not there, Chuuya (you) were crying while you claimed another infidelity

Dazai has to do everything possible to make Chuuya forgive him for so many infidelities and he has to change so he is no longer unfaithful.