482. 3. Double adultery is the adultery of a married man with the wife of another, or vice versa. We call this double adultery, because it is committed by each of the two and the covenant of marriage is violated on both sides. Therefore it is doubly more grave than the first kind.

We said above (no. 480) that following the pledge and covenant, the conjugial love of one man with one wife unites their souls; that this union is the love itself in its origin; and that adultery closes it off and stops it up, like one who closes off and stops up the source and flow of a spring. It is clearly apparent that the souls of the two unite when love for the opposite sex is confined to one of the sex - as happens when a young woman has pledged herself wholly to a young man and the young man conversely has pledged himself wholly to the young woman - from the fact their two lives unite, consequently their souls, because these are their life in its beginnings. This union of souls is possible only in monogamous marriages or marriages of one man with one wife; but not in polygamous marriages or marriages of one man with more than one wife; because in the latter love is divided, in the former united.

Conjugial love in this, its highest seat, is spiritual, holy and pure, because the soul of every person from its origin is celestial; consequently it receives influx from the Lord directly; for it receives from Him a marriage of love and wisdom or good and truth, and this influx makes the person a human being and sets him apart from animals.

[2] From this union of souls, where it is in its spiritual holiness and purity, conjugial love flows down into the life of the entire body and fills it with blessed delights, so long as its course remains open, as is the case in people who from the Lord become spiritual.

Nothing else closes off and stops up this seat, source, or wellspring of conjugial love and its flow but adultery, as is apparent from the Lord's words, that only on the ground of licentiousness is it lawful for one to divorce his wife and marry another (Matthew 19:4-9); and from this statement in the same passage, that whoever marries her who is divorced commits adultery (Matthew 19:9). When, therefore, this pure and holy wellspring is stopped up, as described above, it is, like a jewel in excrement or bread in vomit, encompassed by foul pollutions that are altogether opposed to the purity and sanctity of that spring which is conjugial love. From that opposition arises coldness to the marriage, and in the measure of that coldness the libidinous lasciviousness of licentious love, which spontaneously consumes itself. This is a sinful evil, because it covers over something holy and thus obstructs its course into the body, allowing something profane to take its place and open its course into the body, so that from being heavenly the person becomes hellish.