One of the least flexible rules in many Christian churches is about divorce. The only reason for it is adultery:
And Pharisees came up to him and tested him by asking, "Is it lawful to divorce one's wife for any cause?" He answered, "Have you not read that he who created them from the beginning made them male and female, and said, 'Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh'? So they are no longer two but one flesh. What therefore God has joined together, let not man separate." They said to him, "Why then did Moses command one to give a certificate of divorce and to send her away?" He said to them, "Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so. And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery" (Matthew 19:3-9, English Standard Version, emphasis mine).
Seems pretty cut-and-dry, eh? Who knows how many Christian men and women have lived through loveless and/or abusive marriages because they've been told leaving their heartless spouse is a sin.
Well, in his Christianity Today article from 2007, David Instone-Brewer suggests that instead of giving a simple, cold hard rule Jesus was choosing a side in a much larger debate in Judaism at that time. As such, perhaps it isn’t just adultery that warrants divorce. Please give it a read with an open mind…things may not be as black-and-white as they have seemed: