I recently watch a documentary about sociopaths and it was maintained by the behavioral analyst, psychologist and sociologist involved, that there ARE some with these tendencies who do fall in love. Those who love them back, who truly understand them, understand that they can't control their minds and compulsions. So, I believe there's a small part of Kang Moo that might actually love Kirin or understands (to a point) that someone loves or cares for them. It's not necessarily all one-sided love.