Marriage is one of the most, if not the most important relationship one will enter into in his life. When the LORD created the woman from one of the ribs of the man, and brought the woman to Adam, the bible records these words: And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man. Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh (Genesis 2:23-24). The idea of becoming "one flesh, (figurative)" in the marriage relationship shows the absolute completeness of the union. This union is a sexually intimate attachment (of which the sin of fornication is avoided) to one another as well as being of one mind and judgment in regards to loving and providing for each other for a lifetime. Such should be done according to God's standard (not man's) of right and wrong (Proverbs 14:12, I Peter 3:1-7). However, in many sad cases, this holy union is abused, and the will of God for them is neglected, which results in "divorce". So, what does God have to say about this?
In Malachi 2:16, the LORD expressly says that He hates divorce (New King James Version). Divorce, which in most cases is the result of unfaithfulness or lack of commitment from one or both partners, is hostile to the very nature of God, who is faithful in all things (Deuteronomy 7:9, I Corinthians 1:9; 10:13, I Thessalonians 5:24). There is one exception to God accepting the divorcing of a spouse, which I will now speak about.
In Matthew 19:1-9, Jesus, is speaking to the religious leaders (Pharisees) of His day and His disciples about what God's will is concerning the marriage covenant. In reverting back to God's original plan for marriage, He put to rest a lot of the opinions that was prevelant during that time concerning the bases of divorce (vers. 3-6), which was for just about any reason. So, particulary in ver. 9 of this chapter, Jesus sets boundaries for divorce by saying: And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery. The "putting away" here refers to divorce, and so is translated in th New King James and New American Standard Versions. So, we can see that Jesus says that there is only one exception for divorce, and that is sexual infidelity (fornication) by one's spouse. A divorce, which is done on any other bases, doesn't severe the union in God's eyes (despite society saying it's valid), and to enter into a new relationship would constitute an adulterous relationship. The one who divorced his partner because of his sexual infidelity is the one with the authority to remarry in this instance.
When one finds out that he is in an adulterous relationship, what should he do? The bible makes it clear that God will judge those who are committing adultery ( I Corinthians 6:9-10, Hebrews 13:4). Just as with other sins, the only option one has is to repent, which is having a change of mind about your sins, which results in a change of conduct. Ending the affair may be very difficult, but the LORD promises that your repentance and you giving your life to Him for Heaven's sake will be much greater than anything you have to give up in this life (Roman 8:18, 2 Corinthians 4:17, Philippians 1:23). Also, in repentance, one should seek reconciliation with his first spouse (which is the one God truly recognizes). If this isn't possible, he has to remain celibate in his obedience to God (I Corinthians 7:10-11).
Also, I will note that the bible makes it clear that a marriage covenant is ended when one of the partners die (Matthew 22:30, Romans 7:I-3, Corinthians 7:39). This also gives one the eligibility to remarry without his relationship being adulterous.
When reading this, one may think that God's law on marriage, divorce, and remarriage is pretty "strict". Jesus and His disciples would agree with you (Matthew 19:10-12). However, His law on this subject being "strict" reflects the absolute beauty and holiness of marriage. These are only a few of the many passages that speak of the blessedness of being married (Proverb 5:18-19; 18:22; 19:14, Hebrews 13:4). In most cases, the problem comes in when one has married for the wrong reasons and previously missed all the marital red flags, and excused their mates by saying, "marriage will change things for the better". You can check out an article by Wayne Jackson entitled: "Foolish Reasons for Getting Married" at www.christiancourier.com Also check out one written by Mark Dunagan called: "Marital Red Flags" at www.beavertonchurchofchrist.net .
In concluding, it is always my prayer that one can not only have a happy marriage, but live for God in all things. You would be supremely blessed by the LORD, if you believe in Him, seek Him, and obey Him (Mark 16:16; Acts 2:38; Hebrews 5:9; 11:6). If there are any questions about this, please respond back. If it is the case that I can't answer your question "definitively", I can direct you to others who can help you.
Thanks For Your Time