The speaker describes a "little star" who sleeps beside them, but the poem hints that she appears only in dreams. By day she vanishes, and the speaker is left knowing they will miss her until night comes again. The line "it's only in my dreams we ever meet" confirms what the earlier verses suggest: this closeness is real only while the speaker sleeps.
The feelings are mixed. The speaker wants her there, yet asks her to "leave tomorrow, not today," as if even the dream carries a quiet dread. The "tiny nightmares" that light the way and the "dark-pale gray" she sees suggest the speaker feels flawed or troubled, and that she sees them in a softer, more forgiving light. Going back to bed as soon as they get home, behind "walls of red," shows how much the speaker longs to return to her. The mood is tender and lonely, a gentle sadness with a little comfort inside it.