I think this song is about a girl (Taylor) who goes somewhere for a summer, like a vacation, and she meets a boy and falls in love with him. But then she has to go back to where she really lives and the boy can't go with her, and she's sad. Sh'es thinking of moving on because she can't see the boy, but she loves him to much. At the end of the song it says, "And I'm back for the first time since then". I think that means she's finally back at the boys house, but she thinks he has a new girlfriend so she doesn't want to talk to him. So all she does is leave a letter on his doorstep reminding him of that summer and promising him that even if both of them move on and fall in love with other people, she's still always ggoing to remember him and love him.