1 Corinthians 7:10

And unto the married I command, yet not I, but the Lord, Let not the wife depart from her husband (KJV)

Then: Paul is always careful to match his advice with the Lord's commandments. Addressing the wife first, Paul clearly shows his knowledge of Jesus' teachings by attributing this statement about divorce to him (Baker, p. 102). If either the husband or the wife "puts away" the other, he or she commits adultery (Mark 10:11-12). Jesus does allow it in the instance of fornication (Matthew 5:32). Paul considered the law to be paramount whether one of both spouses were followers of Christ.

Now: Few individuals view marriage as God's plan for spiritual growth. Rather than practicing love and forgiveness in a specially designed laboratory, they prefer to abandon the situation. Often they plunge into another, similar situation which again reveals the need for spiritual growth.

Extra source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.