The obligations of married partners include being faithful and pure in their lives.
74 Behold, verily I say unto you, that whatever persons among you, having put away their companions for the cause of fornication, or in other words, if they shall testify before you in all lowliness of heart that this is the case, ye shall not cast them out from among you;
75 But if ye shall find that any persons have left their companions for the sake of adultery, and they themselves are the offenders, and their companions are living, they shall be cast out from among you.
76 And again, I say unto you, that ye shall be watchful and careful, with all inquiry, that ye receive none such among you if they are married;
77 And if they are not married, they shall repent of all their sins or ye shall not receive them.
President Harold B. Lee said:
“Satan’s greatest threat today is to destroy the family, and to make a mockery of the law of chastity and the sanctity of the marriage covenant.”
(Teachings of Presidents of the Church: Harold B. Lee , 187.)