The diffrence ~ Black Butler ~ Sebastian x Ciel

Ciel Phantomhive is the owner of the Funtom toy company. He has a Demon Butler known as Sebastian Michaelis, who has made a contact with Ciel. If Ciel were to accomplish his revenge on the people who killed his parents, Sebastian could have Ciels Soul... But it seems that they have fallen for each other... what will they do if Ciel accomplishes his goal?