Celestia was beautiful, there was no doubt about that, but she lacked something that he could not put his hoof on.
He remembered the first time he saw her. She was standing on the balcony, wings unfurled, head held high. The moon was slowly rising over the kingdom, illuminating her turquoise mane, and reflecting off of her glossy coat. Her cutie mark shone like a jewel, emblazoned across her flank. Even from a distance, he thought he could see her eyes twinkle.
He was only sixteen years old, but he knew right then that she was the only mare for him. He could love no other.
He also knew that the chances of him marrying such a pony were between slim and none. Regardless, he went back to that bench every night in hopes that she would appear. Sometimes she did, most of the time she did not.
In time, he learned how to tell if she would appear. The faster the night came, the less likely he was to see her. Once, the moon rose in a half hour, and the stars lit up almost simultaneously. He did not see her that night.
As this ability to determine the rate of the moon’s ascension became second nature, he started to appreciate more and more the sky over which it ruled. Daytime was fine, the sun rose, the sky was blue, puffy clouds moved overhead; but it was at night, enveloped in its peace and tranquility, that he could let his eye control his mind and let the two run wild.
Maybe that was what made her far more attractive.
Celestia controlled the day. She controlled the more interesting night.
--
A month later the Royal Guard set up a recruitment booth at his school, and he realized that was his best chance to meet her. The booth itself was an abject failure; the two ponies manning it merely stared strait ahead. They did not look at any of the colts that stopped, and they definitely did not answer any questions. In fact, they did not talk at all.
He was the only colt to enlist, and he only did it because he knew that guardponies were allowed around the royal sisters. If he could not marry Luna, at least he could protect her.
Eighteen months later, he found himself standing on the parade ground among a class of 136 other recruits, listening to Princess Celestia congratulate them on their accomplishment, and charge them with their duty.