"I believe that's rather common knowledge, isn't it?"

That incubi and succubi feed off of sex.

"Human--their minds, emotions, and dreams--produce an energy on which incubi feed. Sex is one of the more direct methods. If you're trying to ask whether I'm holding myself back in the regard or something, I'm not."

He quite simply can't feed in his normal manner. The rules of this world don't allow for it.