He was a noble he's never done any hard labour in his life he couldn't even manage his own money and estate properly and moveover he had been turned to an omega which made it extra harder
No he wasn't mentally ill. That was the punishment he gave himself for getting Rafael killed. He wanted to feel the pain he caused Rafael and his unborn, Klopp, & Rafael family. So he intentionally decided that path for his atonement.
In the novel Klopp isn't beating random people to extort how violence he can be. It's because for some odd reason he feels he needs to kill them and he doesn't even know why he hates them.( Well it's also revealed in the novel that those people he killed & beat in the slums were the ones who harm Aeroc in the first timeline. Those people beat,Rape and harm Aeroc in some way so it's kinda like vengeance for Aeroc. But of course he doesn't know cause it's a different timeline.)
Thank you, this is the most logical answer, honestly so many things are untold in the manhwa but is explained in the novel.
The first season was just straight up suffering. He was selling himself for bread and he got multiple pregnancies and miscarriages because of that. He got pregnant way more than just 5 times. It was unreal because, was he mentally ill that he couldn't do hard labor or work a different job instead, hell he could have been a rich man's side hoe instead of peddling his ass to the lowest. Also damn kloff is habitually going to the slums to beat "rabid dogs" just goes to show how violent he is.