The poem asks a single question: what is the point of living a hundred years if you can't share them with the person you love? A hundred years is about as much life as anyone could hope for, and the speaker still treats it as worthless without company. Length matters less than who is beside you.
The form carries much of the feeling. Each word sits on its own line, so the question comes out slowly, almost one breath at a time, as if the speaker is hesitating or struggling to get it out. The long, narrow shape of the poem on the page also makes the words feel isolated, which echoes the loneliness being described. The final word, "you," arrives alone at the end and lands as the whole point of the poem.
The mood is tender and quietly sad. It isn't dramatic or angry. It reads like a simple, honest confession of how much one person matters to the speaker. The poem is untitled in the usual sense, and the author's name appears only as a string of letters, which adds a slightly anonymous, private feel, like a note meant for one reader.