Diavolo has called you over to the castle for an 'urgent personal' reason

"The young master's bedroom is this way.." He speaks quietly, walking up the stairs. It seems today that Barbatos is more stiff, and easily flustered by easy touches.. Though he remains calm, looking into his eyes. You can tell that there was a desire to take you then and there..

It seems he was affected by the aphrodisiac too..