The speaker moves from uncertainty about whether someone loves them to confidence that the feeling is real. At first, they eagerly wait for a letter or visit; later, they ask for the person to return and stay, not just appear briefly. The repeated joyful refrain makes the change feel energetic and almost overwhelming.
“Walking on sunshine” is a metaphor for feeling extremely happy, as if love has lifted the speaker above ordinary worries. Waiting by the mailbox suggests how much they look forward to hearing from the loved one. The request not to come back only “for the weekend” implies a wish for lasting commitment rather than a short reunion.
The lyrics sound certain about the love, but they also show that the speaker has been waiting and may still be hoping for the other person’s return. So the happiness could reflect a relationship that now feels secure, or the excitement of believing it is about to become secure. The repeated declarations emphasize the speaker’s mood more than they explain what has happened between the two people.