Infidelity (noun)

The action or state of being unfaithful in marriage or a romantic relationship.

Origin:

From latin infidelitās ("unfaithfulness"), from in- ("not") + fidelitās ("faithfulnes.s")

Examples:

1. The infidelity of his wife was a major factor in his decision to divorce.
2. The infidelity of the politician was widely reported in the media.
3. He was unable to forgive her infidelity.
4. The movie was about a woman who discovers her husband's infidelity.
5. The infidelity was discovered when she found a love letter in his pocket.