Bro he was ready to let him.go so when did he finally SNAP
Probably throughout the years of abuse, as he was willing to let SM go during Ch.40 however probably due to palace drama someone hanging someone (which I think it’s either the eldest princes lover or the eldest prince killed the 2nd prince) where CG realizes he cannot live through this hell without SM but this is just my hypothesis on the alluded images that we were given so far ╮(￣▽￣)╭ so take my opinion with a grain of salt. Because at the end of season 1 we see the eldest prince coming back to the kingdom which I’m assuming his lover and CG quoted it along the lines of something reappearing if I’m correct. But overall I’m assuming he lost his mind due to his brother and father abuse.
If you’re asking a specific EVENT I do not know in which we all have to see when the author releases more chapters but if anything it could have been the death of the 2nd prince
I think we all agree that Chang-gyeon has every right to kill his second brother, matter of fact put in his first brother as well who wasn’t able to protect him from the violence and abuse their second brother put him through...reading the trauma and the abuse Chang-gyeon went through he deserves to be a villain and he has every right to destroy the kingdom that ignored his existence and trauma.
This does not excuse the abuse he put Sam-myeong through but this explains his obsessive tendencies towards Sam-myeong, Sam-myeong was his light and happiness in that horrible place his only will to live, and the kingdom took that away ( more so his father). In which he then had to live with an abusive brother and a neglectful father where no one shows him an ounce of care or love in which he endured for YEARS... essentially living in darkness waiting for the light to arrive which is Sam-myeong but we all know he didn’t come back for 20 plus years ( I think)...
Reading it like this explains Chang-gyeon obsession and why he’s such a prick and all I can say is damn and I cannot wait to see how this season ends as much I feel sorry for Chang-gyeon, Sam-myeong does not deserve that treatment and essentially Chang-gyeon is putting Sam-myeong through the same abuse he experienced throughout the kingdom.