Despite his failures, the speaker apparently does not give up hope. Earlier, he had straight up said all that we see and seem is just a dream within a dream.
Here in the poem's concluding lines, which repeat the refrain, the speaker phrases it as a question.
Then again, maybe he's just getting a bit desperate and having a "say it ain't so!" moment.
Even after all the sand has run through his fingers, and even after all his weeping, the speaker can't bring himself to declare that all that we see and seem is but a dream within a dream.
Perhaps he doesn't want to acknowledge the loss of the things in life that have slipped through his fingers—the sand, his ladylove. Maybe he's afraid that none of it was real in the first place. Either way, he's not exactly pumped about life at this moment.
This second stanza looks a lot like the first. It's chock full of rhyming couplets, with a trio tossed in there (in lines 16-18). Only this time, the trio's smack dab in the middle of the stanza, rather than at the beginning, and the second stanza has an extra two lines tacked on. Be sure to check out "Form and Meter" for more.