Is a brother obligated to boycott his brother who committed adultery with his wife? Is such a boycott considered a severing of kinship ties? And is it necessary to inform the adulterous brother that his brother is aware of his crime?

Adultery is a grave sin, and its sinfulness is compounded if the adulterer is a relative or a neighbor of the victim. If it is proven that a brother has committed adultery with his brother's wife, then it is permissible, and may even be obligatory, to shun him. This is not considered a severing of kinship ties. As for informing him of the matter, it depends on what serves the best interest. If not informing him would lead to missing the benefit of shunning him, then informing him is preferable. And if a wife's adultery is proven, it is not permissible to have intercourse with her until her womb has been cleansed. One must be careful not to be lenient in allowing foreign men to enter upon women to prevent discord and immoralities.