That depends on the relationship. A long-term, functioning marriage (or other long-term, functioning, committed relationship)? Sure. No question. Someone I've been dating for a while and it's not clear where the relationship is going? Nope. Men (or women) come and go; your career is your career.
Keep in mind, also, that you are talking about a "dream job" that you don't really know anything about, just something that you have thought about as a possibility in the future, something you think you might like. Not the next logical step in your established career, something you've been working toward for a long time, or anything like that.
I will go ahead and say, because I'm sure someone else will soon if I don't, that, if this guy is a keeper, he will be willing to try to work out some kind of compromise/accommodation to support your career goals (as you will be for him, if you
are "a keeper"
). If the beginning and end of the conversation is "I don't ever want to live in a big city," that tells you something important about him right there.