1. Not "in order to not suck blood". Doyoon has to take "essence" from humans via sex because he is a half vampire that CAN'T suck human blood. Blood doesn't satisfy him the same way it would a normal vampire.
2. The director probably either had someone watching Doyoon or was doing the watching himself. He was already aware that Doyoon was up to something because of how shifty the latter was acting, and Doyoon's blond friend had briefly noticed someone following them when they were together on multiple occasions (c13p12, c13p33-34).
3. Considering the luggage trolley and décor (c14p11), Doyoon went to sleep in a hotel lobby, and since a person-shaped shadow was cast on him when that clingy one-night stand of his left, what apparently happened was that the director appeared and took him.
4. It's unlikely that the man knew the director.
Can someone please explain the main points. So Doyoon is a half vampire who needs to have sex in order to not suck blood? And in Ch14.. how did the director find him?? And take him? Did he know the man?