
I get the reasons why it was hard to say "I left because my bro raped me and he planted the spies and tried to do it again" and to be honest he might have turned all jealous and crazy anyway, but it always drives me nuts when it's not mc's fault and they don't explain themselves

Well, it's probably very hard on Heun coz the lives his entire clan sits on his shoulder. One wrong answer, could mean the elimination of his entire family, their retainers, & the subjects who live on their land. So I would not blame Heun for not trying to explain, when the cost is so great. It's a very dicey subject too, with dirty secret that could shame the family, plus the bad blood between the clan & the emperor could cause the emperor to not believe him. With the emperor already in rage about possible treason/tryst, Heun thought it was best to just keep his mouth shut. Sigh...

Sure tail me detective I’m going to fuck this guy you’re into in my car

The case regarding Kirin's sister was dropped bc there was pressure from families with money and political power. After that, the members were killed, hence no pressure from their families. From the beginning, Kirin admitted to the detective that he got involved with Moo. The detective felt a responsibility towards Kirin since he was in charge of his sister's case, hence he was not okay with Kirin going for revenge, because that was very reckless and dangerous. The evidence they found during investigation indicates Moo is the mastermind behind the murders, and allegedly with Kirin's assistance. Of course he would do everything he could to solve the case and get Kirin away from Moo. There's absolutely no suggestion that the detective is in love with Kirin whatsoever. You're being biased against the detective because you like Moo, however, from an objective point of view, what the detective is doing is 100% reasonable and normal.
Did he awaken something he couldn't handle