To me, this song is about someone who was let go in a relationship. They loved the other person so much that the relationship's end devastated them. How can they love ever again? ("Why a broken dream can never fly?") Why would such a great love end? ("But you don’t know why.") Why can't they be back together? ("All the time you keep believing,"). The person cannot let go of the thought of the relationship. It would hurt too much to do so. The speaker doesn't quite understand why this is so, hence the repetition of "I don't know why."
To me, this song is about someone who was let go in a relationship. They loved the other person so much that the relationship's end devastated them. How can they love ever again? ("Why a broken dream can never fly?") Why would such a great love end? ("But you don’t know why.") Why can't they be back together? ("All the time you keep believing,"). The person cannot let go of the thought of the relationship. It would hurt too much to do so. The speaker doesn't quite understand why this is so, hence the repetition of "I don't know why."