But when Aymeric barges in his office flinging accusations at him while refusing to disclose how he came to know about all those things he comes to the conclusion that his trust in WoL was misplaced and proceeds with his plans of Ascian annihilation alone.

He knew what awaited him if he would do it a deemed dying by our hand an acceptable price to pay for having one less Ascian around.
https://youtu.be/iZNm1pF-kbs?t=18698
"I am become a god.."
"Your contempt for man has proven your undoing. For my first act as god-king, I sentence you to death"
"Seeds of chaos, I shall excise them with my divine blade and bring order to the world"


https://www.youtube.com/watch?v=iGi1YPELLFQ
"Fight me if you will, Warrior of Light. I care not, all who stand against me will be destroyed, be they servants of Light or Darkness" "By my blessing, all men shall be sanctified, and an endless era of peace begins, and conflict shall cease to be."


https://www.youtube.com/watch?v=TUncyDO8CPY
"How can this be? A millennium of prayer and the Eye's powers combined, and yet you still stand?"

Why are you so intent on portraying Thordan as some suffering misunderstood hero who sacrificed himself to destroy a singe Ascian, when the game makes it quite clear he's for power over all of mankind?