What is the ruling on informing a brother about his wife's adultery with him after she seduced him, and what is the ruling on shunning this friend after learning of his deed?

The friend must repent sincerely, for adultery is a grave sin, and corrupting his brother's marriage bed is even more heinous. He must shun indecency by avoiding mixing freely and by being careful with speech and glances. He should remember the words of the Prophet, peace and blessings be upon him: "Beware of entering upon women," and his saying: "The in-law is death." As for informing the brother, the principle is to conceal a Muslim's faults, unless he is known for corruption, because informing the husband might threaten the stability of homes. If he is sincere in his repentance, he has the means to keep the woman away from himself, and informing his brother might not be effective and could lead to great harm. If he commits adultery with a woman and then repents, the husband should not be informed; rather, he should do good to the husband through supplication, seeking forgiveness, and giving charity, for adultery involves the right of Allah and the right of the husband, and it is akin to slander. If the questioner is certain of his friend's sincere repentance, he should remain with him and remind him of Allah; otherwise, he may abandon him.