Under blossoming lilacs, a speaker makes an impossible, tender promise: “Now that I have met you, I must live forever.” The phrase “I said, believing it” matters—the speaker knows, on some level, that no one lives forever, yet the feeling is so strong that it feels true. Love here becomes a demand for more time, as if meeting this person has made life too precious to lose. The lilacs reinforce that mood: they are beautiful and sweet but bloom only briefly. If “Fifty” hints at the speaker’s age, that only deepens the sense of mortality. The poem’s mood is intimate and hushed, full of affection and a slight ache, because the wish to live forever is really a wish not to leave this person or this moment.
Fifty — Summary
I said, believing it, as we stood beneath lilacs:
"Now that I have met you, I must live forever."