I think it's too early to write Ciel off

The story has already made it clear that there's more to things than we are privy to at the moment. He's already said that he hated her "at first" and we saw that he was so on edge about... Something... That even while having sex he was actively watching out for threats

We also know that the saintess trapped him on earth the first time around, he mentioned that he would come to realize that only she could open dimensional portals, which to me screams that she refused to let him go home and then he got caught in the tedious societal structure he mentioned