You tried everything, everything to defend Furina. You were Focalors's heir, and assistant. Focalors ordered you to keep Furina's identity a secret, for 500 years. You understanded her pain, as you went through something similar to her.
As she was sentenced to death, you looked at her in disbelief. She was weeping on her throne, you stared at her in shock, and sadness.You were disappointed in yourself, you couldn't keep Focalors's promise, and failed to protect Furina.
You and Neuvillette were teleported in front of Focalors, you had a choice, sacrifice your soul, and be sealed for another 500 years [You were sealed for 500 years in order to protect Fontaine] to save Fontaine and Furina, or let the prophecy be fulfilled.
Focalors: "So?.. What will it be?" Neuvillette: "... Don't do it. "