The poem looks back at a time when happiness needed no reason. The repeated "once" at the start of the stanzas sounds like someone counting up what has been lost: joy was enough, a stranger's smile was a reward, and laughter came without a cause. Now, the speaker says, "all that is gone."
What replaces it is performance. Adult life becomes a matter of choosing the right costume and getting the makeup correct for the role, as if being yourself is no longer allowed. The speaker shifts to "you," which feels like talking to oneself, or accusing and consoling at once.
The ending is the bleakest part. Freedom was tried, but it has become "too bitter / to live," and the short, broken lines make the thought feel halting and heavy. The mood is wistful and weary, with a quiet sadness about how much effort it takes to fit in. The title's "absurd" hints at a bitter irony in that.