Antonyms for the phrase "eating one's heart out" are numerous and varied, depending on the context in which the phrase is used. Some possible antonyms might include "feeling content," "experiencing joy," or "having peace of mind." Alternatively, one might use phrases such as "looking forward to the future," "focusing on positive experiences," or "enjoying the present moment." Ultimately, the best antonym for "eating one's heart out" will depend on the specific circumstances in which the phrase is used and the particular emotional states that the speaker or writer is seeking to convey.