255. (19) Adultery is ground for divorce. There are many explanations for this which appear in the light of reason and yet today lie hidden. From the light of reason it may be seen that marriages are sacred and adulterous affairs profane; consequently that marriages and adulterous relationships are diametrically opposed to each other; and that when opposite acts upon opposite, one destroys the other even to the last spark of its life. This is what happens with conjugial love when a married man deliberately and thus purposefully commits acts of adultery. These considerations come more clearly into the light of reason in the case of people who know something about heaven and hell. For they know that marriages have their origin in heaven and from heaven, whereas adulterous relationships have their origin in hell and from hell. Thus they know that the two cannot be combined, as heaven cannot be combined with hell; and that if they are combined in a person, immediately heaven withdraws and hell enters. [2] It is on account of this, then, that adultery is ground for divorce. Therefore the Lord says:
...whoever divorces his wife, excepting for licentiousness, and marries another, commits adultery.... (Matthew 19:9)
He says a person commits adultery if he divorces and marries another "excepting for licentiousness," because divorce for this latter reason involves a full and complete separation of minds, which is properly called divorce. But all other cases of divorce on their own particular grounds are properly separations, which we have already discussed just above. If after such separations a person takes another wife, he commits adultery. Not, however, after divorce.