Dreams opens on a blunt statement: dreams never last. From there the speaker drifts through what a dream can hold, visions of the future, visions of the past, even other versions of how life might have gone. The word "dreams" seems to cover both sleeping dreams and the hopes and memories we carry around, and the poem treats all of them as fragile.
The most striking image is "the reverb of your last laugh," still humming "between the cracks." It suggests someone lost or gone, whose laughter lingers faintly in the gaps of everyday life. The speaker isn't wailing about it, though. The tone is quiet and a little worn, like someone who has accepted a hard truth.
The ending widens the idea. Some moments should be grabbed, others let go, but all of them pass, whether good, neutral or bad. The mood is wistful and calm, with a thread of comfort: if nothing lasts, then the painful moments fade too.