I think marriages fail because intending couple refuse to enter into proper and sincere relationship with God and each other. Those who build their marriages on the foundation of sexual sin eventually find themselves outside the grace of God. Many who fail to prepare very well jump into marriage and eventually jump out frustrated. The marriage covenant should be entered into with full awareness and Gods abiding grace.
If couples are not well groomed in certain marital issues before they get married, such as domestic responsibilities (cooking, cleaning, washing etc), communal prayer, deprivation of sex among them and mutual love in the absence of these, such marriages tend to fail.
Marriages fail because couples fail to prepare adequately for marital life. They occupy their time and resources in chasing after the things that do not matter in the marriage. Some couples prepares so much for the wedding day without a corresponding preparation for marital life. There is need for a spiritual preparation through prayer and fasting, this will bring the couples into a closer union with God and each other thus a family that prays together stays together. God should be the center of very marriage.
Most of the marriages are bewitched mostly by girls who are desperate to marry rich men. Most of them attend fake churches where the general overseer will tell the desperate ladies to bring the name of the man or his picture, so that,they will invoke the spirit of the man, after that the man will start Without solid investigation. Love and understanding keeps marriage.
Marriages fail for many reasons depending on the couples involves and the culture they come from. But a novel tendency which I'd insidiously and aggressively destroying the institution of marriage is the "ideological theory" which objectifies the conjugal love thereby alienating the place of God in marriages. Thus ,any marriage deprived of God is bound to fail.
Marriage fails in various ways but the fundamental cause should be misunderstanding, lack of trust, pride lack of love humility and listening ear, and accepting rumors without solid investigation. Love and understanding keeps marriage.