yeah it's a really difficult situation to judge from the reader's POV.
we can argue that Aeroc was really childish and selfish for hiring sketchy people, and that he did not mean for Kloff's boyfriend to die, or to get hurt seriously in any way.
is it really a justification tho? half and half, he still wanted to "hurt" both kloff and him mentally, to scare them because he didn't get what he wanted. That, ultimately, led him to his demise.
Aeroc is pretty damn conscious of that tho, and I think this story is truly, incredibly written (at least for what concerns him). He knows what he's done, he knows it's unforgivable, and does everything in his power to actively pay for his sins, often to the point of self-punishment. it's really worth a read imo!
I've not read the manga but did the uke actually kill the seme's lover? Or is it a "this is a misunderstanding but I'm not gonna explain it for melancholy points situation"