You have lived for thousands of years and have been through more than anypony could realize. The throne was maintained by you alone for one thousand years. You stopped wondering how you brought yourself through each day after the first two centuries. The words of many a diplomat have been heard by your ears when you sat alone.
Just as there were many diplomats, there were many students to pass under your wing as well. Each started out the same in your eye. They were always obedient little shadows, newly bestowed with the title of Faithful Student as they stood in the silver light of your greatest regret and the sunlight that you bring.
Two graduated successfully, becoming as close as to gods as ponies could be. Others quit, some failed, and others became monsters. Each and every one of them had something in common despite the different paths each was lead on.
They all saw you smile, and what a pretty smile you have, and a truly disarming one at that! Not a single one left your side and hardly any came close to learning what is beneath the serenity you have recovered is this millennium. It was because of these Faithful Students, the private pupils that rose above all the others in the academy you founded, that you were only alone if you stopped to think.
It doesn't matter if the room is crowded or empty, a single stray thought or pause in your performance and you will realize just how alone you feel. You would know exactly why you do not tell anypony if you hadn't denied anything was wrong and sealed away even the mere acknowledgment of your problem.
You have even forgotten what's wrong haven't you? Luna's return is not a guarantee that your behavior will get better, but it is only with your careful and dedicated management that it has improved at all. Surely, you at least know what this problem involves? This isn't a borderline occurrence any more.
You aren't healthy. You may have defeated many tyrants in an age that has since passed but you are the tyrant of your own mind. You still numb your heart to what has been going on and still you haven't realized that you are the greatest villain that there is.
Tirek stole the magic, but you cripple your own now, when millions of ponies depend on you. Discord overthrew the first nation of Equestria set up by the newly unified tribes but he never wounded anypony as deeply as you wound yourself.
Only the Crystal Empire's overthrown king is worse than you for he has spilled blood wantonly.
You still think of life in two absolutes even if you have lessened the strict observance of your morals.
You continue to betray yourself and those you suffer for it. Your kindness, a trait that earned you an Element of Harmony, despite how unreliable yours can be. Your subjects adore their image of an altruistic and peaceful ruler, but you are only the reflection in the mirror.
You're the only thing you have ever run from. Why can't you face yourself? Why seal yourself away? I'm only you.
You listen so much to everypony, but seem quite deaf yourself even though you have to know I'm here to push yourself away. If you keep this up will there be any thing left? Why do you ask questions if you stopped seeking answers?
Are you lying again? When will you tell the truth? When will you tell anypony?
You're so sure that you're perfectly fine and that you'll never have another outburst or fight with Luna again like you did a millennium ago.
You've waited and waited and waited, smiling all the while and even though you've tried you have only tried to cover up the problem until there's only your own denial left.
I'm you. I'm the things you'll never know, you'll never say and you'll never realize that you feel. Or, to put it correctly, I used to be you. I was a piece of the puzzle that when correctly built formed you, Celestia. Currently, I am but a buried and broken aspect of you. The small pauses you make in the halls when you catch yourself with a thought that doesn't feel like you, or at least not the you that Celestia wants to be. Now I'm only that, your illusion, your denial, a simple little voice that sprung from the divide you lay within yourself.
You are not a victor; you haven't escaped anything.
It's only missed opportunity to get better, but I think that after all these years you've made it quite clear that none of that matters to you.
So go ahead. Teach more Faithful Students, appreciate the happiness that comes from learning the true nature of your Elements only after Luna was gone and know that I can only get you when you're awake like this. If you want happiness to last this is a botched job.
Break your promises. Avoid honesty. Be as kind to everypony who lives under the rule of Luna and yourself while trying to hold onto your mask for that much longer, just don't forget how cruel this is to yourself. Tell everypony how happy you are and maybe it'll be true when they leave you to pursue their own lives. Go on feeling empty when they grow up and you still refuse to tell a single soul about any of this. You still think there is nothing wrong. You don't know why you can feel so empty at times because you don't want to.
"It's all in my head" has gotten you this far. Ignoring it has gotten you this far. It's also made everything worse.
Just go on distracting yourself since now all this light is only meant to blind yourself and others from the darkness within you.