Breathe. He needs to be calm and be able to think now, he can be sad later. Leareth breathes in and out and pulls even further away from the tangle of emotions, and then he can formulate words and speak them again, with the downside that it feels kind of like he's floating and the speaking part is happening a long way off.
"Urtho was my teacher when I was a child. In my first life. Afterward I went back to my home kingdom and - rose in power, was an advisor to the King - he disapproved of my ambition - and then we were at war. I know I did not want to go to war, but. I tried to win, I was winning, and then - he did a Final Strike to destroy his own stronghold so my army could not take it, and he - deployed a powerful magic weapon, of some kind, that I had not known existed, and sent a strike team with it, and they killed my first body. And nearly destroyed the world."
He takes a slow unsteady breath. "I was - thinking of that. When Mhalir asked me what I would do, in the Yeerks' position. And I thought that I would surrender. It is not even a hard choice. Winning the war with Urtho, keeping my kingdom and all its progress, was not worth the cost of escalating, when he had such a weapon. And that the same held for the Yeerks. That - not losing to the Andalites - is not worth the deaths of five billion people."