Well, that made me cry. Good story. So she did, truly die?

Vibe checked

"It is such a quiet thing, to fall. But far more terrible is to admit it."

Living forever is a curse, a curse that forces you to see your friends die, your decisions worsen, your health deteriorate.

The underlined portion is antithetical to the rest of the sentence. Perhaps you meant mental health?

I tried to fly to where I couldn’t breathe, but my lungs simply filled with infinite air.

That carries a lot of interesting implications.
If you put an alicorn into outer space, would the vacuum of space fill? Would the stars consume all of the new fuel at once and expand to destroy everything? Alternatively, would an alicorn increase the air pressure of their resident planet simply by existing? Would the pressure increase so much that the air starts to seperate into its resident components, and subsequently change into a liquid, or even solid state? Is Equus now a gas giant?
Is it in our solar system? Are we right down the cosmic lane of a mass grave? Are the alicorns still there, in one of those very planets, wailing an eternal dirge in the chaotic storm of their own tragic nature?

Celestia, Celestia it seemed to call out. And I must admit, for a minute I was unsure. Through all my bravado, jumping a hundred feet would cause anyone to run away. I closed my eyes and imagined the screams that the ponies would bellow out. Seeing their princess plummeting down to her “death.” Their princess who has sentenced many to die despite their lives, murdered in cold blood, played and manipulated while pretending to be pure. I made up my choice. The ground was real.

Well, at least she confessed her sins before she died.