The antonyms for the phrase "keeping forever" include the following terms: short-lived, temporary, fleeting, impermanent, transient, evanescent, momentary, brief, ephemeral, and passing. These words describe the opposite of the idea of "keeping forever"; they imply that something does not last forever or for a long time. Short-lived things might last only for a short period, while ephemeral things may exist for just a moment. Temporary and transient objects could last for a little while, but not permanently. Therefore, these antonyms provide a useful contrast to the idea of "keeping forever" and describe a sense of fragility and impermanence in life.