In the most general sense, this song is about having a secret that one can't or doesn't want to share. But, I think it is specifically implying a scenario where two people have a secret together and even though they go about their daily lives, they each equally have that secret on their mind, and yet they do not share.
In the most general sense, this song is about having a secret that one can't or doesn't want to share. But, I think it is specifically implying a scenario where two people have a secret together and even though they go about their daily lives, they each equally have that secret on their mind, and yet they do not share.