I think it's about a girl who lives in her dreams/thoughts and goes to this place in her mind where everything is perfect, but the place is behind all the walls she's built up because of her insecurities, and her lover can't follow her there, because she won't let him past her walls. I think the song is saying that he just wants her to let him in; he wants her back in reality and to realize that she doesn't have to hide there.
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