Well, besides the obvious. Some think that she and Twilight were Celestia's first and only students, others the latest links in a long chain. But at least it can be proven she had two - which is more than can really be said for friends, lovers or children.

So has she been alone the past millennium? Or lonely in a different way, living on while those close to her did not? What do you think?

Students she's had aplenty - although she regrets that the days when she ran her school as closely as Cheerilee are far behind her, she's had a personal apprentice or two more often than not over the past few centuries. (The Sunset-Twilight gap is unusually short, especially if you count Cadance, but these are hardly normal times.) Often these students graduate into her close friends, but she also has a knack for finding new ones in every corner of Equestria, generally when she least expects it.

Lovers (don't ask me what kind) she takes on average once a century (discounting that one century as skewing the curve) but their names are never publically known at the time (and generally not in their lifetime). No offspring are known to have resulted from these unions, and "everypony knows" that the Princess treats all her little ponies as the children she cannot bear herself - Mother to the whole nation.

Yeah, I think after the first few centuries, she probably starts distancing herself from ponies. She'd have had students, confidants, people like Star Swirl in her life who were important, but as they age out of it, she takes up more and more of that eternal matron illusion. Lovers I could see, but few and far between, long enough for her to forget the hurt and heartache before she starts all over again.

I didn't want to answer this question at first, because it sounds like an excuse to just talk about your OCs. :P

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Well, if you have any interesting ones...

8. Other than Twilight, Luna, and Cadance, what relationships have been important to Celestia in her lifetime (students, close friends, lovers, family)?
There was Sunset Shimmer, of course. I think Celestia has had other students as well. I'm not sure Celestia's ever allowed herself a true friend other than Luna.

Post-2014 addendum: And now we know she also had a mentor figure in Star Swirl.

Everyone. Not everypony: everyone. She holds the universe in her heart. She prefers to be around those who try to come to understand what she has come to understand, so she has spent more time with Twilight, but she loves everyone.

I like to imagine that she had a normal childhood once. A very, very long time ago. Little Tia learning to run around, scraping her knee. Growing into her rebellious 'I know better!'-phase, and later into her 'It's not a phase!'-phase. Before eventually, she matured beyond 'regular' maturity. We do see her having a mischievous streak that she apparently usually hides quite well.

In 'my' version of this world, she is revered by many as this almost god-like figure. Because at the end of the day, she simply is one. She wields powers beyond comprehension and her body is durable in a sense that blood, flesh and magic alone cannot explain. But she has seen what happens to those entities that lose themselves, that lose their connection to the world they were born into. And while she is painfully aware that, with infinity stretching before her, she cannot escape such a fate forever, she still fights to keep that day far off.

The best way to keep yourself centered and tethered is to participate. To experience to the fullest and feel, to renew yourself a little each day. I see her taking on many students over the centuries. She teaches them as much as she learns from them. An old spirit might grow stiff. This proximity to youth helps with that.

In the same vein, so do lovers. She doesn't force anything, obviously. And she is careful with who she picks and lets in. Her position comes with many risks, after all. Liars seeking power or wealth. Fanatics idolizing the 'perfect' leader. While she might, or might not, be what they want and see in her, what she wants is simple: To be seen, and treated, as a somewhat normal pony.

Something that became more and more difficult as the centuries passed by. Their rule wasn't flawless, but it was good. They won their battles. They led their ponies to safety and wealth and prosperity. And more and more, their ponies started to put them up on those dreaded pedestals. They were the ones putting distances where she tried to have none.

Still. On the odd occasion, somepony challenges what became the new status quo. Somepony wants to know more. Learn more. Get to know her better. Not just the leader, the goddess, but the mare that seems to know all the blends of tea in existence and yet sticks to the most basic ones as her favorites.

I see her having partners. With such a long life, you obviously start to think in different timespans. To take a couple of decades to properly process your grief after a loss due to age or other reasons seems less notable.

And then the rift happened. Luna fell, and all of a sudden, she stood alone. I like to think she had families before. Bloodlines that trace back to these days, before Luna's banishment. Blueblood, that cesspool of 'friendliness', actually hired historians and scholars, spending a good amount of his family's fortune to prove that he is, much to everypony's annoyance, a distant descendant of one of her spouses. I think she monitors her own bloodlines to a certain extent. Just out of curiosity, by this point.

But after Luna's banishment, there was little else than grief. This was a loss felt much, much deeper than the losses she had before. It wasn't just family she had lost. Worse, actually - she had attacked herself. What now loomed over her was a frightening prospect. Something she and her sister had managed to ignore, helping each other out in that regard: Loneliness. Without Luna by her side, she now truly stood alone on top. With nopony who truly understood her, as nopony shared her fate.

While the pain might have dulled over decades and centuries, certain... defensive mechanisms were raised. To a certain extent, she distanced herself further. Equestria still needed her. Or rather, Equestria still needed The Princess. The leader. And with an entire nation depending on her leadership, there was little she could do to tend to her bleeding heart.

Luna's return finally started a very painful process of healing. Those wounds will inevitably leave scars. You don't suffer loneliness for a thousand years without traces of it remaining, even thousands of years after the healing has finished. I like to think that in this millenia, when she stood alone, she developed a certain... passivity. A knack for scheming. Nudging small pieces and, given her extensive experience, predicting the outcome. I don't think she ever manipulated anypony with malicious intent. But I do think that she manipulates. A lot. We all do, obviously, but she is more aware of it and of the consequences of each word and gesture. This insight allows her to steer things in certain desirable directions. Probably something Luna, after her return, finds a little disturbing.

Welp. That was a massive tangent and yay, parts of what I just wrote even answered parts of the question. Whoop whoop!

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Quite an answer! So for you Luna's loss changed her a lot... well, I think we all think so, but the question is how. I think you have her before close to how I have her more recently.

And yes, she can be rather manipulative - generally to what she sees as the manipulee's good, or at least the greater good. She's got so good at it it often works, too... which might lead her to overlook if it's truly the best idea. (After all, she never really bore Honesty...)

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Well, yes, I ramble a lot. (Should I bow or apologize? Joke. Just a joke.)

Not sure if this is the right spot for that, seeing as I seem to have a tendency to answer questions in threats that don't ask that information, yadda yadda, thing is:

In my head-canon, I vastly expand on the dreamscape as its own realm with its own flow of time and its own laws. And its own denizens. Nightmares are creatures. Some of these denizens are symbiotic, some parasitic. They leech of the dreamers' emotions. Which, you know. Not always a bad thing. A dreamscape creature might devour the dreamer's fury. That's a good thing. He goes to bed very angry after that massive tiff with his special somepony, but he awakes and finds himself strangely bereft of that anger. Wasn't so bad after all. Making up with him/her will surely be nice, though.

It gets problematic when these dreamscape creatures become smarter. Not all are. The smart ones are few and far between, and they are the real danger. They are called 'farmers'. Because they had a funny idea: "If I feed on anger, I have to scour the dreamscape for it to find angry dreamers. And once I devoured their anger, I have to find new angry dreamers. WHAT IF... I make them angry?" They attach themselves to dreamers and start manipulating their dreams. They try to foster dreams that fulfill their appetites. Which might have funny consequences if a farmer yearns for arousal or joy.

Problem is-... well, I guess it's a good thing for ponykind, actually. They don't really understand the world outside the dreamscape all that well. They can access the dreamer's memories, but they usually don't understand much of what they see there. Which doesn't make for the most successful dream manipulation.

And then, there was Celestia. A pony so deeply hurt, so lonely, so stricken by grief that she was a massive bonfire within the dreamscape, luring any and all creatures there that were interested in what her tortured mind had to offer. And after a century or two of infighting, one creature emerged victorious. A farmer. Massive and greedy and strong. It attached itself to her dream. It observed. Fed. Learned. And over a couple more centuries, crafted the perfect nightmare to torture her. To make her bleed more. To keep the dream steady and reliable. Wouldn't wanna wake her up screaming now, would it? That thing grew even more massive due to her. And there was no Luna around to challenge it. To rid her sister of this parasite.

It was defeated, eventually, of course. After Luna's return and some shenanigans. But the damage was done.

And yes, she can be rather manipulative - generally to what she sees as  the manipulee's good, or at least the greater good. She's got so good at  it it often works, too... which might lead her to overlook if it's truly the best idea. (After all, she never really bore Honesty...)

Yes. So much yes!

She does have 'her little ponies' best interests' at heart. At all times. But yes, honesty wasn't her Element. Neither was Laughter or Loyalty. In a very sad way, that's telling. She could really have used the former. And things might not have escalated with the latter. But oh well, things are how they are.

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An interesting untold tale - her own counterpart to the Tantabus, perhaps even worse.

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Yes. I suppose one could argue about what's worse. I don't intend to. It was bad. Both scenarios are bad. Unhealthy.