I bet someone tried to put the moves on him and he just didn't notice. Or he noticed, totally freaked out about how he would be taking advantage of them because of all his powers as a duke etc. etc., and shut them down but good.

Then probably he went to his room and fretted about the possible latent rapist tendencies he might have inherited from his father. Meanwhile, downstairs, the young lady in question shrugged her shoulder and had a short but satisfying fling with Sebastian.