(Col 2:13,14.   Heb 8:13).

"Therefore, what God has yoked together
let no man put apart."
 (Matt 19:6).

A woman under a vow to Almighty God by The Christ's subjecting of her can only remarry "if her husband dies."* (Rom 7:2,3). Otherwise, she commits bigamy. Further, if sexual relations take place with another man, it is adultery. The same is the case for a man who remarries while his wife is still living. And if adultery takes place while the spouse is living, there are no grounds for reconciliation. This is because he/she is defiled, something detestable before Jehovah, even under Mosaic Law.  (Deut 24:4).

If a woman obtains a certificate of divorce solely under manmade law (and from an unwilling husband) she has broken her vow in respect of Christ's Law, unless on account of fornication. And if she does obtain a certificate of divorce, she still cannot remarry, even if adultery is proven against him or he voluntarily gives her a certificate of divorce. If a woman commits adultery (sexual relations outside marriage) she cannot then be made a "subject for adultery" having already fornicated. But  if one divorces a spouse for some other reason and/or fornication, and decides to marry another under the delusion that his or her divorce is within the arrangement of God and permits remarriage, they are both "subjects for adultery". Divorcing on grounds other  than fornication makes one a "subject for adultery". (Mark 10:10-12)  (Matt 5:31 34 Moffatt).

The act of sexual intercourse itself and marriage generally is  not becoming "one flesh". (Gen 2:24). Becoming "one flesh" is through the procreation of a child from the flesh of the husband and the flesh of the wife.  They become one through procreation.  (Matt 19:4-6).

FORNICATION: Voluntary sexual intercourse between man (occasionally restricted to unmarried man) and an unmarried woman.
ADULTERY: Voluntary intercourse of married person with one of the opposite sex other than his or her spouse.
BIGAMY:  Having two wives or husbands at once.

"In his saying "a new covenant" he has made the former one obsolete. Now that which is made obsolete and growing old is near to vanishing away."  (Heb 8:13).

"For instance, a married woman is bound by law to her husband while he is alive; but if her husband dies,* she is discharged from the law of her husband. So, then, while her husband is living, she would be styled an adulteress if she became another man's. But if her husband dies, she is free from his law, so that she is not an adulteress if she becomes another man's."  (Rom 7:2,3).

"You heard that it was said, 'You  must not commit adultery.' But I say to you that everyone that keeps on looking at a woman so as to have a passion for her has already committed adultery with her in his heart… Moreover it was said, 'Whoever divorces his wife, let him give her a certificate of divorce.' However, I say to you that everyone divorcing his wife, except on account of fornication, makes her a subject for adultery seeing that whoever marries a divorced woman commits adultery."  (From Matt 5:27-32).

"That is why a man will leave his father and his mother and he must stick to his wife and they must become one flesh."  (Gen 2:24).

"To the married people I give instructions, yet not I but the Lord, that a wife should not depart from her husband; let her remain unmarried or else make up again with her husband; and a husband should not leave his wife."  (1 Cor 7:10,11).

Issuing a certificate of divorce to a spouse who has not committed adultery is a serious sin. For it is the same as stating publicly that he or she had fornicated, as it is only on the grounds of fornication that a certificate of divorce can be issued under the Law of Christ. (Matt 5:32). Remarriage by divorcees while their spouse(s) are still living is double adultery.