Divorce from the bonds of matrimony may be obtained for any of the following causes:
1. Insanity existing for 2 years prior to the commencement of the action. Upon this cause of action the court, before granting a divorce, shall require corroborative evidence of the insanity of the defendant at that time, and a decree granted on this ground shall not relieve the successful party from contributing to the support and maintenance of the defendant, and the court may require the plaintiff in such action to give bond therefor in an amount to be fixed by the court.
2. When the spouses have lived separate and apart for 1 year without cohabitation the court may, in its discretion, grant an absolute decree of divorce at the suit of either party.
3. Incompatibility.