I think it is about a summer romance that he was not expecting, that he wasn't ready for. His friends tells him that he can either have her or not have her. So he has to make a decision. He's unsure at first, but as he spends more time with her, he realizes that he really wants to be with her. He falls in love with her and thinks she also loves him. He realizes that she is very kind and her kindness also helps him make his decision. At the end of the song, he makes his decision that he wants to be with her. So during the rest of the song he is with her. She moves him along all during the rest of the song. Then at the end, the summer ends, and she "disappears" and then the songs ends with him realizing that he wont see her again but he loves her. And the last line explains that he is not ready to be in love.