You may be just "one" in this world, but you may as well the one's world, and you know you love the layout when you want to be happy, even if that means being happy that you are not part of it.
You may just be "the one" in the world but you may be the world's one and you know you love someone when you want them to be happy. Even if their happiness means. You do not have to be a part of it.
You may only be one person in this world, but you may also be the world to one person, and you know that you love her when you want them to be happy. Happiness means. That you're not part of it.