no, karl "ruined his own life" (not that it is ruined) , he's an adult with tons of possibilities at the time thanks to julian, but instead he chose to pursue a man who, thanks to trauma, mental disorders and skewed power dynamics (that karl is all aware of), can't possible be in a healthy relationship with him.
it was his choice to be with sascha, stop him from running away multiple times, protect him from prison and from war, sascha didn't ask him to sacrifice himself like that as far as we know nor ever gave him much false hope. they both don't owe each other, but karl definitely had more free will and options than sascha to let this love go, since for sascha it meant the dangers of the duke and living on the street etc.
that said, historically he would be drafted into war anyway, and most soldiers pre ww1 saw it as their job and duty to go anyway (before mustard gas and the horrors of ww1), so i personally don't think much of him going to war (which karl choose too bc he didn't want to leave sascha alone while in prison for 25 y...)
i feel bad for both of them, but karl definitely isn't an innocent victim of sascha, if at all of his own obsessive love for him, since he had a lot of choices. and war was the fate of millions anyway
The way some readers are saying that Sasya is playing the "victim card" when he's probably clinically depressed and was sexually assaulted in the past like, god forbid he has trauma from that and isn't able to support or sustain a healthy relationship with someone else rn I know he did Karel dirty but he's literally mentally ill- someone get them both a therapist