Re: question
Sebastian's feelings mostly amount to creepy possessive stuff like "how dare you separate me from him" and "I want him right where I can watch him". The month or so he's been in the game is pretty much no time at all from his perspective, so he hasn't really moved on from "I want out of here this is a hindrance to my goal" yet that most characters get over in, what, a matter of hours. It's not really enough time for him to start missing anyone - he's still adjusting to suddenly being able to do his own thing again after years of mostly only following orders, and at present he's not very happy about having to, as he views it, fill up his days with time-wasters.
If he were to spend months and months in Kiseki without Ciel he'd probably start to enjoy the freedom a bit more, and while he wouldn't really miss Ciel, who is an insufferable brat most of the time, he'd miss having someone to be an openly snarky jerk with. For now there have been a fewtimes when he's made dumb demon jokes and then went "...oh ):" because Ciel wasn't there to groan at them. Seriously.
His creepy possessiveness aside, he'd rather spend years in Kiseki alone than have Ciel arrive, because Kiseki is obviously stronger than him and he does not appreciate the thought that he wouldn't be able to protect Ciel from its shenanigans.
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Does Ao have any deep thoughts (relatively speaking) on Kiseki and the people she's met so far? Is there anything about it she doesn't like?