"Eat one's heart out" is an idiom used to express envy or jealousy towards someone or something. Its antonyms could be contentment, satisfaction, and happiness. These words indicate that the individual is satisfied with their own situation and doesn't feel a need to envy or be jealous of someone else's accomplishments. Another antonym could be indifference, implying that the individual does not have any emotional investment in anything that might provoke envy or jealousy. Other antonyms for "eat one's heart out" could be admiration, appreciation, and respect, indicating a positive attitude towards another individual or accomplishment rather than negative emotions like envy and jealousy.