The speaker is near death, and the poem is a quiet accusation aimed at someone who isn't there. Three promises are listed in a row: to stay until the end, to leave marigolds on the grave, to dance until their legs gave out. Each one is small and loving, and the marigolds, chosen because they were the speaker's favorite, show how personal the promises once were.
Then the poem turns. "And now," sits alone on its own line, like a pause before bad news. The speaker is "almost six feet under," a blunt phrase that makes the approaching death feel close and real. The final question, "Where are you?", is short and plain, and it carries the hurt of the whole poem.
The mood is lonely and sad, but not loud. There's no shouting, just disappointment and a hint of disbelief that someone who promised so much could be missing at the moment it counts. The poem suggests that broken promises hurt most when they're the ones meant to comfort us.