Matthew 19:9

I tell you. Here is Christ's law. And she has not been unfaithful. "Unfaithful" means guilty of a sex act involving someone rather than her spouse. [This would apply to the husband as well; and would include sex acts between woman and woman; between man and man; and between a woman and a man who are not married to each other. The technical term is "fornication."] Commits adultery if he marries some other woman. Because where the spouse was not "unfaithful," the original marriage bond is not broken. Alford (Greek Testament) says: "Notice, as on ch. 19:32, APOLELUMENEN without the art., and thus logically confined to the case of her who has been divorced ME EPI PORNEIA [not been unfaithful]. This not having been seen, expositors have fallen into the mistake of supposing that the dictum applies to the marrying a woman divorced EPI PORNEIA [because of unfaithfulness], which grammatically would require TEN APOLELUMENEN. The proper English was of rendering the word as it now stands, would be, a woman thus divorced, viz., ME EPI PORNEIA [not been unfaithful]." A man who divorces his wife in spite of the fact that she has not been unfaithful to him, and marries another commits adultery, because he is still married to his former wife; also, if anyone marries this divorced woman, who was not unfaithful he marries another man's wife. [For a special case, see 1 Corinthians 7:15.]