It is the only ending yes, but it is actually not so sad (it is, but not super sad). You see in the dreams (memories of the black phoenix girl) that a human (with a suspicious haircut) is best buddy with a minotaur. They take part in the war and live happily ever after, when the human is named headmaster of Secat's Academy after building the big golden door that you open during the game.
The "afterlife" you describe is that past. The phoenix girl sent you back in the past to save you.
Viewing post in Game ending【spoilers】
I played Fae's Last Flight a long time ago, but I thought that as one of the earliest games made, its content was not about the storyline of Monster Girl Academy.
So was the old man who was locked on the cross at the beginning the protagonist of the Monster Girls Academy game? Even after being sent back, he was still captured by the demon? Isn't this too unfortunate?
Is this series hopeless? Are the troublemakers destined to succeed and rule the world, while the protagonist controlled by the player must only be their plaything? I want to see the failure of these villains, and I want them to pay the price for their actions and suffer severe punishment😡😡😡.
More importantly, I really want three succubus sex slaves😋😋😋.