I think it is about a girl who realizes her lover isn't all she thought he was. He let her down and ruined their chances for that desired "happy ending". She realizes that he's no prince charming or knight in shining armour. He won't swoop her off her feet and carry her away.
He comes back asking for forgiveness, but it's too late to come and rescue her. As much as she wants to go back to him, it's too late for him and his white horse to come around.
I love this song!
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