Speaking as a man, I can tell you that there is no “right way” to be asked this question. “How do I fit in your future plans?” is a question that is loaded with danger to most normal men – especially if they’ve heard it before.
So here’s a question for you, instead: “Where do you want the relationship to go?” I suggest that you just tell him that, and ask him if he agrees, or would like to discuss it.
My first observation is made partly in jest. The question puts the onus on the man to go out on a limb – before you have given any indication of your own, other than “the relationship as it is” – to make a commitment to you or to leaving. Why not take the bit here and state your own declaration? See how that feels. (I’m not saying that in a nasty way: “There, now, see how that feels!” Rather, I’m suggesting that you take cause over the relationship; be the leader; say what you want, and invite him to sign on to your plans, if he’s not making any of his own.) See how it feels.