13 Wherefore they who say that the marriages of such are not marriages, but rather adulteries, seem not to me to consider with sufficient acuteness and care what they say; forsooth they, are misled by a semblance of truth. For, whereas they, who of Christian sanctity marry not, are said to choose the marriage of Christ, hence certain argue saying, If she, who during the life of her husband is married to another, be an adulteress, even as the Lord Himself has laid down in the Gospel; therefore, during the life of Christ, over Whom death has no more dominion, if she who had chosen His marriage, be married to a man, she is an adulteress.
They, who say this, are moved indeed with acuteness, but fail to observe, how great absurdity in fact follows on this reasoning. For whereas it is praiseworthy that, even during the life of her husband, by his consent, a female vow continence unto Christ, now, according to the reasoning of these persons, no one ought to do this, lest she make Christ Himself, what is impious to imagine, an adulterer, by being married to Him during the life of her husband. Next, whereas first marriages are of better desert than second, far be it that this be the thought of holy widows, that Christ seem unto them as a second husband.
For Himself they used heretofore also to have, (when they were subject and did faithful service to their own husbands,) not after the flesh, but after the Spirit a Husband; unto Whom the Church herself, of which they are members, is the wife; who by soundness of faith, of hope, of charity, not in the virgins alone, but in widows also, and faithful married women, is altogether a virgin. Forsooth unto the universal Church, of which they all are members, the Apostle says, “I joined you unto one husband a chaste virgin to present unto Christ.” But He knows how to make fruitful, without marring of chastity, a wife a virgin, Whom even in the flesh itself His Mother could without violation of chastity conceive.
But there is brought to pass by means of this ill-considered notion, (whereby they think that the marriages of women who have fallen away from this holy purpose, in case they shall have married, are no marriages,) no small evil, that wives be separated from their husbands, as though they were adulteresses, not wives; and wishing to restore to continence the women thus separated, they make their husbands real adulterers, in that during the life of their wives they have married others.
Source: On the Good of Widowhood (New Advent)