That he might seek a godly seed. Therefore take heed to your spirit, and let none dead treacherously against the wife of his youth. There is only one lawful cause for divorce and remarriage. All other grounds for divorce and remarriage are unlawful in the sight of God. That one scriptural grounds is fornication, not just adultery.
Fornication is any form of illicit sexual intercourse.
It would not only include adultery but also include sodomy, incest, and beastality. All adultery is fornication, but not all fornication is adultery. Only the innocent part may be free to remarry without sin- a. if they have been innocent. Those who are the guilty party, or those who divorce for any cause, are guilty of sin. Those who marry one who has been put away as a guilty party, or one who marries a person who has divorced for any cause, are guilty of committing adultery.