The revolutionary general's wife is young and beautiful. Since he is about to be executed for treason, her life is going to change a lot. She will likely be imprisoned or tortured to reveal what she knows about her husband's activities—e.g., other conspirators in the rebellion, etc.. As a woman, she is also vulnerable to sexual assault in this situation. To protect her from this harsh life, her husband murders her instead. A sexist and rather antiquated notion of honor, but one that prevailed in the time and place that this story is set.