(1) If the other spouse has committed an act of un-chastity;
(2) If he or she has been deserted maliciously by the other spouse;
(3) If it is unknown for three years or more whether the other spouse is alive or dead;
(4) If the other party is attached with severe mental disease and recovery therefrom is hopeless;
(5) If there exists any other grave reason for which it is difficult for him or her to continue the marriage.