The biblical teaching on divorce is fairly straightforward. It was not part of God's plan.
Moses allowed divorce for hardness of heart (Mark 10:5,6). This was sensible. The people he led did not have the cross or the spirit, so they could not live up to God's standards. They need a way out when sin made a mess of their lives.
Jesus was staunch against divorce. His position is based in creation. God has made two people one. There must be no divorce, except in cases of adultery (Mark 10:6-11; Matt 19:9). Adultery destroys the oneness that marriage establishes, so it destroys the marriage. However, Jesus did not cancel Moses' allowance for hardness of heart.
Paul softened Jesus stand by allowing divorce when a person becomes a Christian and their spouse refuses to continue living with them. The Christian spouse is "not bound" (1 Cor 7:15). This means that they are free to remarry (Rom 7:2,3). On the other hand, if the non-Christian is willing to stay, then the Christian cannot divorce. We must note two; things about this.
The expression "be willing stay" is quite strong. The Greek words mean "be glad to make a home with." This is not mere toleration. It means making a home together. If the unbelieving husband were to keep on abusing his wife, she would be entitled to leave.
The unbelieving spouse receives salvations by living with their Christian spouse (1 Cor 7:14). Our individualistic world does not understand the power of this. It is another way of getting unbelievers to heaven.
Paul does not condone divorce where both spouses are Christians (1 Cor 7:10-11).
Paul allows a Christian wife to have a spell apart from her husband, if things are not working out (1 Cor 7:10-11).
The separated wife must try to reconcile with her Christian husband.
If the Christian husband has committed adultery, been emotionally or physically violent, a wife is free to remarry. See Violence and Marriage.
Separation provides an escape for a Christian wife who is being abused by their Christian husbands.
Paul does not offer temporary separation as an option to husbands. He offers women the option of temporary separation, because they are more vulnerable. Christian men do not get this option, because they have economic and physical power. This continues the protections for woman provided in the Old Testament.
The Bible does not have a hierarchy of sins. Sin is sin. Divorce is no better or worse than other sins. The cross can deal with divorce, just as effectively as any other sin. There is no sin too tough for the cross.