"Affaire de coeur" is a French phrase that translates to "affair of the heart," referring to a romantic or passionate relationship. The antonyms for this phrase would be words or phrases that describe the absence of a romantic relationship or emotional attachment. Some possible antonyms could include phrases like "casual encounter," "platonic relationship," "professional acquaintance," or "strictly business." These antonyms suggest a lack of intense passion or emotional investment, indicating a more casual or formal relationship. While "affaire de coeur" emphasizes the passion and intensity of romantic love, its antonyms suggest a more clinical or detached approach to relationships.