Love and LustHis preferences and sexuality.
Tackling Muraki's sexuality from a certainly BL series is quite rather complicated as it shows a side that Muraki is indeed straight, as what nature intended him to be. However, if we're talking about his interests, that would be a different story. Coming from the mangaka's own words concerning Muraki's preferences:
Actually, speaking of that, I got a question asking me whether or not the Doctor liked guys, so I'll answer that here. A) Either guys or girls are OK. If it's a target that draws his interest, he doesn't care whether they're female or male. To the point, he's inconsistent. However, he did have a childhood girlfriend. He's just a difficult guy to understand.
Yep, there we go, he's difficult to understand. The Muraki we see now is bound by his interests, and these interests also involves lust and obsession. Anyone can fall a victim when he got his eyes on someone whether they are either a male or a female, it doesn't matter.
“We men don't have a different feeling that women call love.”
But if we're going to look more closely outside the box, or more precisely, the aspect of love whether he's capable of giving and receiving or not, then we might have a definite answer. Looking at how insane Muraki could possibly be, love would be impossible to cross his mind as he sees this as a human vulnerability. And being a manipulative exerpt that he established for himself now, it would be an admission to weakness and would be a huge threat to his persona. But going back to his earlier years, he had this mystery girlfriend named Ukyou—so for me, it's his defense mechanism not to acknowledge love to avoid ruining his developed madness since he was able to give it before he became what he is now.