unfaithful
Definitions
Not loyal or true to a person, duty, or obligation.
Engaging in sexual relations with someone other than one's spouse or partner.
Not accurately representing the facts or the original source.
Examples
He felt betrayed after discovering his partner had been unfaithful throughout their marriage.
The knight was accused of being unfaithful to his king by conspiring with the enemy.
It is difficult to trust someone who has proven to be unfaithful to their promises in the past.
Synonyms
disloyal treacherous adulterous faithless perfidious untrue deceitful