Fornication and Adultery is Unlawful 17:32
And do not enter into the performance of an action with a woman with other than a lawful intent. Surely it is a disgusting and abominable action and an evil road.
Adultery and fornication have been defined as having sexual intercourse with a woman without a lawful or legal contract. In the Qur'an, Allah says that men who commit fornication/adultery are not to marry any except women who commit fornication/adultery or women who are idolaters. And women who commit fornication/adultery are not to marry any except men who commit fornication/adultery.
Adultery/fornication is an abomination of exaggerated shamefulness exceeding the bounds. So much so, that Allah does not say don't commit adultery/fornication; He says don't go near it. If a person starts moving towards it, that person is becoming weak for the temptation. They are weakening their moral muscle.
Also in the verse mentioned previously, Allah compares adultery with shirk, associating partners with Allah. Adultery is to be unfaithful, disloyal. The adulterer is unfaithful to his spouse while the idolater is unfaithful to his Creator. If a leader is not committed to his community, then he is committing adultery because his commitment is elsewhere. He is allowing the bonds that keep society together and progressing to unravel. A husband committing adultery is unfaithful and is destroying the bonds that hold together the family, the foundation of society.