The phrase "affaires de coeur" refers to romantic affairs or matters of the heart. Its antonyms could be words that connote disinterest or a lack of emotion. Words such as indifference, apathy, detachment, and unfeeling could be considered antonyms. Whereas "affaires de coeur" suggests passion and intensity, these antonyms are used to suggest a lack of emotional involvement or interest. In the context of relationships, these adjectives could describe someone who is emotionally distant or disengaged. In contrast, the antonyms for "affaires de coeur" may not necessarily suggest negativity, but they do suggest a lack of intense emotion or investment in a romantic relationship.