Responses
As the author said it is a happy ending too. I interpret it as as long as Kirin is breathing, Kang Moo won't tether too far where he's not able to go back to him. It's just bittersweet because Kang Moo will ALWAYS struggle to not want to cut someone up. And Kirin will ALWAYS be anxious and live with the fact that his lover is a legit psychopath and all the tendencies that come with it lol.
The condition of socio- and psychopathy always fascinated me. It's interesting how the author chose to make Kang Moo a certified psychopath lol. It's arguably the crazier of the two. She handled it well. Kang Moo as much as he is able too, 'loves' Kirin in his own way. Even if it's not the kind of love we are used too. Kirin knows and accepts it.
Their relationship is bittersweet. Kirin knows if and when Kang Moo wants to act on his impulses, he can't stop him. So they just take it day by day. And that's their warped happily ever after.