Four short lines carry a single joke that is also a confession. The speaker tells the person they love that even stars tumble from the sky when this person walks the earth. It's a flattering exaggeration, as if the loved one's presence is so powerful that it pulls the heavens down.
The real turn comes in the last line, where "fall" changes meaning. Stars fall in a literal, physical way, but the speaker falls in love. By saying it was "impossible not to fall for you," they put themselves in the same company as the stars: both are helpless against this person's pull. The tone is light and playful, almost teasing, yet it feels sincere underneath. There's also a hint of surrender, since falling isn't something you choose. The mood is warm, a little dazzled, and charmingly simple, which suits the idea that the speaker's feelings were never really a decision.