Infidelity can be sexual or emotional in nature. What one perceives as an act of betrayal, another may not. Infidelity is typically defined as unfaithfulness in a marriage or relationship. It can cause a lot of pain and suffering for all involved, and the help of a trained couples counselor who specializes in infidelity can help couples decide if their relationship is recoverable. Sometimes relationships end as a result of an affair, while others survive and may actually grow stronger.