When someone is unfaithful, it means that they have broken trust or been disloyal to someone. The opposite of being unfaithful is being loyal, trustworthy, and honest. These are qualities that are highly valued in any relationship. Being faithful means being committed to one person or a particular group and being dependable. Other antonyms for "was unfaithful" might include "devoted," "true," "dependable," "reliable," "committed," "honest," "trustworthy," "loyal," and "faithful." These words describe someone who is willing to be responsible and honest in any relationship or situation.