I suppose the honor of being your favourite only extends so far as to the final number of masters you've been contracted to.
[After all, being the favourite out of two masters isn't all that impressive.]
[To confirm or deny, that is the question. Though from the way Sebastian sounds, with that tone of voice, Sebastian may have some vague recollection of that night. Ciel knows that playing at self-assurance is a game Sebastian employs, that he may just be fishing for information, so the question is whether Ciel wants to lose his trump card. He decides he does not.
But...Sebastian does not look like he's lying with his last confession, couldn't be either way if he wanted out of this cesspool of sugar. And though Ciel will never admit it, Sebastian's confession fills him with ruthless satisfaction, and no small measure of happiness pride that he's made such an indelible mark on the demon, as Sebastian has made on him. So Ciel concedes to tipping the scale, just a teensy bit.]
Putting aside the fact that I would end you should you leave me, [Ciel looks away, not in shyness but in a struggle to put his thoughts into words, and weighing just how much of his beliefs he should admit to. He doesn't do feelings, okay?] I find myself...likewise. In a tight army of deadly companions, you are the one I desire most at my side. You are useful, though not always correctly obedient. [Sebastian gets a glare for that one.] But you have not betrayed me [yet] and now, are you admitting that you would stay by my side, even if the contract were not forcing you to?