Most Helpful Girl
You can't stop people from asking a question that's actually none of their business, but you can control how you react to their question. Stop letting it piss you off. It hasn't happened yet simply because it hasn't happened yet. There doesn't have to be a reason, it just is the way it is.
Most Helpful Guy
dude, fucking lie about your dating history. You've had a girlfriend.
If you can't make yourself do that, then say "I've been on plenty of dates, I just haven't met a girl I really clicked with yet."