This is called double adultery, because it is committed by both parties, each of whom violates the marriage compact. It is therefore twice as serious as the previous type. We said above (480) that the conjugial love of one man with one wife after their engagement and marriage compact unites their souls, and this union is the very love itself in its origin; and that this is blocked and stopped up by adultery, like water bubbling up and forming a stream from a spring. The couple's souls are united, when sexual love is restricted to one person of the opposite sex, as happens when a girl has pledged herself wholly to a young man, and in return he has pledged himself wholly to the girl. This is obvious from the fact that their lives are united, and in consequence so are their souls, because these are the first beginnings of life. The union of souls is impossible except in monogamous marriages, that is, between one man and one woman; it is impossible in polygamous marriages, that is, between one man and several women, because in this case love is divided, and in the other case united.

The reason why conjugial love in this its highest location is spiritual, holy and pure is that the soul of every human being is in origin heavenly. It there receives direct influence from the Lord, for it receives from Him the marriage of love and wisdom, that is, of good and truth, and it is this which makes him human, and distinguishes him from animals.

[2] From this union of souls, conjugial love, which is there in its spiritual holiness and purity, flows down into the life of the whole body, and fills it with blessed joys, so long as the path of its outflow remains open, as happens with those whom the Lord makes spiritual. Nothing else so blocks and stops up this location, or spring and outflow, of conjugial love as adultery, as is clear from the Lord's words, when He said that only on account of adultery was it allowed to divorce a wife and marry another (Matt. 19:4-9); and also from the statement in this passage that anyone who marries a divorced woman commits adultery (verse 9). So when that pure and holy spring is stopped up, it is, as said before, encumbered with foulness, like a gem surrounded with dung or a loaf with vomit; such foulness is totally opposed to the purity and holiness of that spring, that is, conjugial love. This opposition produces coldness in marriage, and proportionate to this is the wanton pleasuring of scortatory love, which destroys itself of its own accord. This is a sinful evil, because what is holy is covered over, and its outflow into the body is obstructed, and what is profane takes its place and the outflow of this into the body is opened up. As a result the person becomes hellish instead of heavenly.