When it comes to describing a "sexual relationship outside marriage," the context can vary greatly, and so can the antonyms. Depending on the perspective, cultural, and social background, they can range from positive to negative, neutral or judgmental. Some of the antonyms that might fit the bill for this term include celibacy, monogamy, faithfulness, loyalty, commitment, purity, chastity, fidelity, and abstinence, among others. These words describe different forms of intimate or sexual behavior that deviate from the concept of extramarital affairs. While some of these antonyms imply positive values and choices, others may carry a more restrictive or moralistic tone, and the final interpretation will depend on the context and the cultural framework in which they are used.