Betrayal is the breaking or violation of a presumptive contract, trust, or confidence by that produces moral and psychological conflict within a relationship amongst individuals, between organizations or between individuals and organizations. Often betrayal is the act of supporting a rival group, or it is a complete break from previously decided upon or presumed norms by one party from the others. Someone who betrays others is commonly called a traitor or betrayer. Betrayal is also a commonly used literary element and is often associated with or used as a plot twist.
–Wikipedia