Jesus taught several things about marriage, so what was Jesus’ exact teaching on the institution of marriage, remarriage, and divorce?
A Divine Institution
Marriage is not an institution created by mankind. It is an institution designed and created by God, and for the glory of God. After the creation of the universe and all living things, God then moved to create His highest being…human beings, and it was said, that “God created man in his own image, in the image of God he created him; male and female he created them” (Gen 1:27). This was never said about any other creature or created thing. Only male and female are made in the image and likeness of God. God created them in His own image, but isn’t God Spirit (John 4:24)? Yes, but the image God is speaking about is not a physical resemblance but a spiritual one. Mankind can choose, they have free will, they can make decisions that are good and godly. Mankind can think, ponder, plan, decide, and act totally outside of anyone else’s will, so mankind is unlike any other creature God has ever created. He has a conscience. That makes them special, and in the beginning, they had fellowship with God, and God walked with them (Gen 3:8)…until Eve was deceived and took of the Tree of the Knowledge of Good and Evil, and her husband, Adam was not guiltless. He knew God forbid this but took it anyway. He was standing right alongside Eve and said nothing at all, so he has no excuse. Eve was deceived. Adam, not so! Anyway, in the beginning, “the Lord God caused a deep sleep to fall upon the man, and while he slept took one of his ribs and closed up its place with flesh. And the rib that the Lord God had taken from the man he made into a woman and brought her to the man” (Gen 2:21-22), and then the Lord said, “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh” (Gen 2:24). The two are now one…in family, in purpose, and in unity. God created mankind, and then He created marriage. 
Marriage is one of the highest human relationships there are, if not the highest, and it is one that God takes seriously, and He expects us to take it seriously too. Marriage should never be entered into lightly. There must be a long, thoughtful process of counseling, learning about the other spouse’s interests and desires, and there must be a basic understanding about how men and women are radically different from one another. They should know what the expectations of their spouse is. Do they plan on raising their children in the same church, or even having children, and if so, when? Do they plan on living in the country, a small town, or a big city? Do they expect to be at home every night or does one desire to go out more? What are the major differences in lifestyle? This relationship should never be taken lightly but with the forethought that marriage is meant for life. It’s a lifetime commitment to one another made before God and before witnesses. It’s a covenant, so to speak, and both parties are to be committed to the other for life. The Bible teaches that there is only one exception to this, and that is ongoing, unrepentant adultery. Marriage is created by God for the glory of God, and it must be a marriage that is undefiled before God. The author of Hebrews wrote, “Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous” (Heb 13:4). Clearly, marriage should be held in high honor, and the couple must remain faithful to one another. For all others, “God will judge the sexually immoral and adulterous” (Heb 13:4), and that judgment will be fast and furious (Rev 21:8). The church at Corinth had issues with sexual immorality, so the Apostle Paul asks the question, “Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality” (1 Cor 6:9). In fact, we are “not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler—not even to eat with such a one” (1 Cor 5:11). Adultery is a work of the flesh, and “the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God” (Gal 5:19-21).
Jesus on Marriage
Jesus didn’t leave much room for us to justify divorcing our spouse. Just after He said, “Whoever divorces his wife, let him give her a certificate of divorce” (Matt 5:31), He says “that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery” (Matt 5:32). Elsewhere, He says, “Everyone who divorces his wife and marries another commits adultery, and he who marries a woman divorced from her husband commits adultery” (Luke 16:18). Concerning adultery, some believe an addiction to pornography is the same as adultery of the heart, based upon Jesus’ teaching “that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart” (Matt 5:28), but is adultery of the heart the same thing as the physical act? Does a spouse whose mate is addicted to pornography have biblical grounds for divorce? What if the spouse falls and commits adultery one time, but then repents and confesses it to their spouse? Is that grounds for divorce? Of course, the very best thing would be for the offended spouse to forgive their spouse and let that be a life lesson for the spouse who fell into adultery, but some believe, it’s one strike and you’re out. I don’t’ believe this fits Jesus’ teaching that we’re to forgive seven times seventy (Matt 18:22), which means our forgiveness should be unlimited, but on the other hand, if a spouse continues to commit adultery and keeps coming back over and over again for forgiveness, have they really repented of it? These are tough questions that must be sought out, and it will take some time with a good, biblically solid Christian marriage counselor . Your pastor might not be able to handle this, depending on his education and experience. Several people have also brought up Paul’s writing that if an unbelieving spouse leaves, the other spouse is not bound, but this has scholars somewhat divided on it actually being grounds for divorce if the other spouse leaves (1 Cor 7:15).
If you or someone you know is contemplating divorce, and especially on unbiblical grounds, I urge you to speak with them about the seriousness of divorcing a spouse, especially if there is no adultery in the marriage. God will hold us all accountable for our decisions, and He will base His judgment upon Scripture and not human tradition or human reasoning (or excuses). Divorce is always a last option for a spouse being cheated on. Reconciliation should always be on the table. We must leave room for the Spirit of God to work in their lives, if indeed He is in them at all. Satan is always in a hurry, but God never is. Think it through before you divorce. Seek counsel from a professional Christian counselor or pastor. Make sure you have a lot more than accounts or suspicions…they must be absolutely true. Don’t give up on your mate if they are cheating on you. If God can work even in a pagan king’s heart (Prov 21:1), He can work in your spouse’s heart too, or the heart of someone you know who is committing adultery. This doesn’t mean you shouldn’t warn them (Gal 6:1), but after you’ve warned them of what Jesus taught, pray for them, and don’t give up on them…God never gives up on us (Heb 13:5), so we shouldn’t give up on others either.
Here is some related reading for you: Primary Causes of Divorce 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible : English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.