I remember the summer when I was ten years old. The evening breeze gently caressed the green willows and rested on the girl's red hair, sparkling with light. From that day on your life will be eternal for love, even if you die.
"Death, for a sane person, is just another great adventure." Nico said. The same goes for you. Even if you know that you are just a pawn in the war, even if you know that death is the inevitable result, you are still not afraid. You are just moving forward alone, walking alone on the thorny road that Dumbledore pointed out for you. For his own promise, but also for his unwavering love for Lily.
And this love, for you, is also called loneliness.
You used cold words to avoid your fiery heart. Yes, you succeeded. But you seem to have forgotten that the evil mark on your left arm cannot cover up the traces of your love. That noble silver-white deer finally exposed your heart. You said, forever, with long eyes.
When life passed by little by little, you grabbed the boy's arm and looked directly into those green eyes, with light finally shining in them. Through it, can you see the girl with a smile like a flower in the sunset? Can you return to eternal peace with repentance?
If I were to find one word to describe you, I would use eternity.
For Lily, your eternity is your loyal love; for Harry, your eternity is your protection until death. What about you, Severus? If time goes by and everything goes back to the past, do you just want to go back to the girl with the clear green eyes, sit side by side with her under the green shade of the river, and let the afterglow of the sunset pour in lightly, until forever and ever.