情夫 specifically denotes a married woman's male lover. The female counterpart — a married man's mistress — is
情妇 (qíngfù). Both carry strong moral disapproval and appear mostly in court reports, gossip, and TV dramas. A neutral / kinder word is
情人 (qíngrén, 'lover / sweetheart'), which can be used by either party regardless of marital status.
