Because for some odd reason, you're the one she supposed to be with.
It is physically painful watching the two of them circle in messy orbits. The earth and moon spinning and whirling, never once breaking pattern.
The moon consistently looping round and round every day, changing positions every hour on the hour. Full of craters, marked with debris, wholly imperfect, just a ridiculous excuse for a phenomenon that we believe in because we don't know any better. The earth basking in the admiration of the constant moon, reveling in the fact that it is deemed more glorious than the sun or the constellations or the rest of the majesty of the solar system.
To the moon, the earth is all there is. And to the earth, the moon is the one who always has pull on her. They gravitate and fall together without even trying. It's beautiful. It's a rare glory that couldn't otherwise be replicated in science. It's ridiculously dangerous and takes everything. One alteration could be the end of it.
How do I know all this? I am very intelligent, I'm a scientist. And I know this dance better than most, except one.
See, he is the moon and she is earth. And since I've known him, I've watched him circle her. She is the center of everything he knows. The most important thing in his entire universe. She is rare and beautiful and the one constant that he has never been able to get rid of, permanently stuck hovering in her gravity. But, the earth, she is not so innocent.
She has seen a lot, traveling on her orbit around the other glorifying planets and their luminous moons, strong and sturdy asteroid belts, constellations that put her heavens to shame, and the only thing that burns brighter than she ever could. She knows the sun and prefers the moon. The sun knows her beauty and warms to it, but the moon is her only exception. Hers, and only hers.
The moon belongs to earth, and the earth cannot exist without the devotion of the moon. It is such an amazing world that we live in that neither can do without the company of the other. And they thrive on the attentions: pulling the earth's tides, placing stake in the firm crust of the moon's shell, peeking the first rays of moonlight over the earth's treetops, watching the spreading grin of the moon in its face.
Yes, their orbits are permanent despite any and all change in their universe. It's quite remarkable honestly. I've studied theories like this one for years, specialized in them even, and I have never known any waltz such as this. Because for some odd reason, the moon and the earth, they are supposed to be with each other and no one else. Their love is reciprocal, but unlike most things in my scientific world…
They are each other's only exception.
And the other crazy thing about the moon and the earth is that no matter what, he's always going to follow her. He believes in anything that brings him back home to her. He takes up everything he has and goes with her, because it's better by her side.
I don't know what rule or theorem could equate in my world, but I live in theirs.
And he will continue to waltz around her and she will continue to waltz around him, thus continuing their path. Neither one set free from the other's gravity. And just like in science, the moon will follow the earth, never once stepping out of orbit.
Why? She's his only exception.