Husband and wife who are validly married to each other. But if they do not contain themselves, let them marry. For it is better to marry than to be burnt. Until the death of one of the partners. Because the lifetime welfare of the children and of the married couple themselves requires that they be permanently united.
Divine law requires the couple to stay together until death, even if they have no children.
In special cases separation is permitted, but the bond of marriage remains. A union that is a real marriage in the eyes of God and therefore can be broken only by death. No power on earth, therefore, can break a valid marriage. What therefore God hath joined together, let no man put asunder. This includes the civil government.