The phrase "be someone's affair" refers to a romantic or sexual relationship that someone has outside of their committed partnership. There are many synonyms for this phrase, including "have an affair", "cheat on someone", "be unfaithful", "commit adultery", "have a fling", "carry on a secret romance", "indulge in infidelity", "have a clandestine relationship", and "engage in extramarital activity". These words all carry a negative connotation, as being unfaithful to a partner is generally seen as a breach of trust and betrayal. It is important to communicate openly and honestly with partners about one's desires and boundaries to avoid being in a dishonest or unfulfilling relationship.
