3 I find joined to your letter of inquiries a short paper containing the following words: “ask him, (that is me,) whether a woman who has left her husband on the ground that he is an adulterer and sodomite and has found herself compelled to take another may in the lifetime of him whom she first left be in communion with the church without doing penance for her fault.” As I read the case put I recall the verse “they make excuses for their sins.” We are all human and all indulgent to our own faults; and what our own will leads us to do we attribute to a necessity of nature.
It is as though a young man were to say, “I am over-borne by my body, the glow of nature kindles my passions, the structure of my frame and its reproductive organs call for sexual intercourse.” Or again a murderer might say, “I was in want, I stood in need of food, I had nothing to cover me. If I shed the blood of another, it was to save myself from dying of cold and hunger.” Tell the sister, therefore, who thus enquires of me concerning her condition, not my sentence but that of the apostle.
“Do you not know, brethren (for I speak to them that know the law,) how that the law has dominion over a man as long as he lives? For the woman which has an husband is bound by the law to her husband, so long as he lives; but if the husband be dead, she is loosed from the law of her husband. So then, if, while her husband lives, she be married to another man, she shall be called an adulteress.” And in another place: “the wife is bound by the law as long as her husband lives; but if her husband be dead, she is at liberty to be married to whom she will; only in the Lord.” The apostle has thus cut away every plea and has clearly declared that, if a woman marries again while her husband is living, she is an adulteress.
You must not speak to me of the violence of a ravisher, a mother's pleading, a father's bidding, the influence of relatives, the insolence and the intrigues of servants, household losses. A husband may be an adulterer or a sodomite, he may be stained with every crime and may have been left by his wife because of his sins; yet he is still her husband and, so long as he lives, she may not marry another. The apostle does not promulgate this decree on his own authority but on that of Christ who speaks in him.
For he has followed the words of Christ in the gospel: “whosoever shall put away his wife, saving for the cause of fornication, causes her to commit adultery: and whosoever shall marry her that is divorced, commits adultery.” Mark what he says: “whosoever shall marry her that is divorced commits adultery.” Whether she has put away her husband or her husband her, the man who marries her is still an adulterer. Wherefore the apostles seeing how heavy the yoke of marriage was thus made said to Him: “if the case of the man be so with his wife, it is not good to marry,” and the Lord replied, “he that is able to receive it, let him receive it.” And immediately by the instance of the three eunuchs he shows the blessedness of virginity which is bound by no carnal tie.
Source: Letters (New Advent)