Thousands of years later, Estella committed suicide because she didn't want to hurt Xiao Yi. The last sentence is "Sorry, snake. I really want to be good friends with you, so I am a friend. A long time ago, Xiao Yi saved Estella's life.
But because of race, Estella is a human being, Xiao Yi is an inferno (or a demon king), and both Estella's parents were killed by demons, so Estella vowed to kill everything with magic, so she is an enemy.
The details are complicated, so it's better to know for yourself. ...