RPGMemes

I never said anything even vaguely approaching that?

What do you even mean by "told me from the beginning what he wants to do"? If I'm prepping a fantasy campaign and one of my players tells me, "I'd kinda prefer we do something sci-fi" then I have no obligation to change my entire campaign because a player isn't happy with it. I might still do it, if I felt interested in running that and the rest of the table does too, but imo I'm well within my rights to tell him no.

If you mean that he wants a plotline of his own then I'd do my best to accommodate that, assuming it doesn't clash with the rest of the campaign horribly. If it does, then I'd just say that and offer alternatives if I can think of any. If I can't, then of course he can still play if he'd like.