[Spoiler] Drama "Liar"

In the drama, Yoo Yeon-seok's character seems to be set up as someone capable and handsome, so sleeping with women shouldn't be that difficult. It felt like Seo Hyun-jin's character would have ended up in bed with him after just one or two more meetings, so why did he bother using drugs?
Is he a psychopath who enjoys rape? Using drugs doesn't seem like it would make a huge difference...
Or is he an extreme efficiency-seeker who felt that meeting one or two more times was a waste of time?
Even so, I don't understand why he would take such a risk with his son's teacher.
Does he even love his son?
I know he's a bad guy, but he seems like a character that is even harder to understand than other villains.