Marriage and Divorce
The Bible makes it clear that once a man and a woman have consummated their marriage they have become one flesh (Mark 10:7-8).
The man and the woman are bound to each other by the law as long as they live (Romans 7:2) but if one of the members of the marriage dies, the other can go out and marry again (Romans 7:2). However if this is a woman, she must marry a man in the Lord (1 Corinthians 7:39). A man is not to divorce his wife and neither should a wife divorce her husband. If the wife goes out and has sex with another man, she shall be called an adulteress (Romans 7:3).
Romans 7:3 King James Version 3 So then if, while her husband liveth, she be married to another man, she shall be called an adulteress: but if her husband be dead, she is free from that law; so that she is no adulteress, though she be married to another man.
If there is a situation that the woman is going through and she needs to get away from her husband, this is allowed, however she must not get with or marry another man. She is only allowed to separate from her husband, not divorce him (1 Corinthians 7:10-11).
1 Corinthians 7:10-11 King James Version 10 And unto the married I command, yet not I, but the Lord, Let not the wife depart from her husband:
11 But and if she depart, let her remain unmarried or be reconciled to her husband: and let not the husband put away his wife.
According to God's Word, the wife is bound to her husband as long as he lives (1 Corinthians 7:39).
1 Corinthians 7:39 King James Version 39 The wife is bound by the law as long as her husband liveth; but if her husband be dead, she is at liberty to be married to whom she will; only in the Lord.
With that being said, it is important to know the stages of marriage.
There is the espousal stage (also called betrothal), and then there is the consummated stage when the marriage is official by both the man and woman having sex. If a man has a wife in the espousal stage and at the consummation stage finds that she has fornicated before the marriage consummation (Matthew 19:9) he can put her away and write her a bill of divorce.
That is the only case this is allowed.
Matthew 1:18-21 shows this:
Matthew 1:18-21 King James Version 18 Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost. 19 Then Joseph her husband, being a just man, and not willing to make her a public example, was minded to put her away privily. 20 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost. 21 And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins.
At this point when Mary was pregnant with Jesus Christ, Mary was Joseph's espoused wife (Matthew 1:18). Joseph was also considered Mary's husband while she was espoused to him (Matthew 1:19). However, Joseph assumed that because she was pregnant, she had committed fornication before their marriage was consummated. In any other case, he would have been correct, but Mary was with child of the Holy Ghost (Matthew 1:20). Joseph wanted to divorce Mary privately rather than Mary being judged according to the law of Moses.
But after the angel of the Lord explained the situation to him, of course none of that happened.
If a man puts away his wife for any other reason and goes and marries another woman, he is an adulterer. Also, if his wife goes and marries another man, that man that married her is an adulterer while she is an adulteress. She is still her first husband's wife.