The speaker offers a small, almost joking promise: "i would make a really pretty sunset, i promise." On the surface it's playful, but the line carries a quiet ache. A sunset is something people stop for and admire without needing a reason. By saying they would make a pretty one, the speaker imagines being valued in that effortless way, and it sounds like they aren't sure they are.
The word "promise" is the telling part. Nobody needs to promise a sunset is beautiful, so the speaker seems to be pleading, maybe trying to convince someone, or themselves. The lowercase letters and the casual tone make it feel like a private thought, half-embarrassed and half-hopeful.
The line above it, "du verschwendest deine zeit 57" (German for "you're wasting your time"), seems to work as a counterpoint, a dismissive voice that the speaker answers with this tender, vulnerable line. The mood is wistful and fragile, softened by a little humor.