Chương 30: Memory Eater?

Actually, what happened there was not what Richard had planned from the very beginning. 

He never wanted to have sex with Henry. Neither he asked him to remove clothes to have sex nor he drugged Henry.

He wanted to scare Henry and humiliate him. That's why he asked him to remove clothes to see his helpless face. But he realised he had lost control and got closer to him. He shouldn't be doing that. He should not play dirty. 

He didn't want to be so intimate with Henry. But it happened when Henry begged him to touch him more.

He lost control...

It could say Richard took advantage of his weak state. 

He kinda regretted it though. He thought it was unlike him to take advantage of a weak guy who can't even think straight. 

As for the drug, it was actually not a drug. It was a side effect of what Richard did to him. He knew this was coming. But he just got interested to watch how Henry would struggle when he wanted pleasure. He wanted to bully Henry to get his revenge.