As a people, they had joined themselves to strange gods. This was spiritual adultery. Their unfaithful spirit showed in their marriages also. As they put away God, so they were putting away their wives. Covenant breakers on one level of relationship will break covenant on other levels of relationship.
Divorce spells unfaithfulness, treachery, betrayal, and love grown cold.
God wants people who are faithful, true, and constant in their love. In many ways the spiritual stature of people can be measured by the way they act in their marriage. God's attitude toward divorce is demonstrated also in that, although He permitted divorce under Moses, He forbade it for the priests. Again, God hates divorce.