“Neither can it rightly be held that a husband who dismisses his wife because of fornication and marries another does not commit adultery. For there is also adultery on the part of those who, after the repudiation of their former wives because of fornication, marry others. This adultery, nevertheless, is certainly less serious than that of men who dismiss their wives for reasons other than fornication and take other wives. Therefore, when we say: ‘Whoever marries a woman dismissed by her husband for reason other than fornication commits adultery,’ undoubtedly we speak the truth. But we do not thereby acquit of this crime the man who marries a woman who was dismissed because of fornication. We do not doubt in the least that both are adulterers. We do indeed pronounce him an adulterer who dismissed his wife for cause other than fornication and marries another, nor do we thereby defend from the taint of this sin the man who dismissed his wife because of fornication and marries another. We recognize that both are adulterers, though the sin of one is more grave than that of the other. No one is so unreasonable to say that a man who marries a woman whose husband has dismissed her because of fornication is not an adulterer, while maintaining that a man who marries a woman dismissed without the ground of fornication is an adulterer. Both of these men are guilty of adultery” (Adulterous Marriages 1:9:9 [A.D. 419]).
“A woman begins to be the wife of no later husband unless she has ceased to be the wife of a former one. She will cease to be the wife of a former one, however, if that husband should die, not if he commit fornication. A spouse, therefore, is lawfully dismissed for cause of fornication; but the bond of chastity remains. That is why a man is guilty of adultery if he marries a woman who has been dismissed even for this very reason of fornication” (ibid., 2:4:4).
“Undoubtedly the substance of the sacrament is of this bond, so that when man and woman have been joined in marriage they must continue inseparably as long as they live, nor is it allowed for one spouse to be separated from the other except for cause of fornication. For this is preserved in the case of Christ and the Church, so that, as a living one with a living one, there is no divorce, no separation forever” (Marriage and Concupiscence 1:10:11 [A.D. 419]).
“In marriage, however, let the blessings of marriage be loved: offspring, fidelity, and the sacramental bond. Offspring, not so much because it may be born, but because it can be reborn; for it is born to punishment unless it be reborn to life. Fidelity, but not such as even the unbelievers have among themselves, ardent as they are for the flesh. . . . The sacramental bond, which they lose neither through separation nor through adultery, this the spouses should guard chastely and harmoniously” (ibid., 1:17:19).