In recent news from Germany a female legislator wanted to create a legal "trial marriage" of sorts, one that expired after 5 years or so. I don't think that the idea passed, but it shows the attitude of our world towards this sacred institution. What grounds are legitimate in our fallen world then? Although this is not the only passage on the topic, I want to focus on Jesus' statement in Matthew 19:9. Here the only legitimate grounds for divorce are porneia in Greek, broadly translated by sexual unfaithfulness. Divorce in Jesus' day was apparently as easy or even easier than it is today, so we cannot really excuse their society or ours. The only difference was perhaps that in their society, divorce was more often a male prerogative. What is important is the comparison between the phrases "one flesh" and "sexual unfaithfulness." One or other marriage partner has broken the sacred bond. What Jesus did here was demand a complete rethink of what marriage is. The failure ought not be the norm. Divorce ought always have the status of being a lesser evil, never an ultimate good.
Reference: The Gospel of Matthew, New International Commentary on the New Testament, NICNT, by: R.T. France, Wm. B. Eerdmans Publishing Co. 2007