Am I being selfish? Wedding issues?

I've been engaged since early March. We're getting married in August. My brother and his girlfriend just got back together after being broken up for two months, and they're apparently talking about marriage. Not engaged, but "talking". She's already picked a day, two weeks after mine. She asked if I would be okay with that, and I said no, frankly, I'm not. Am I being a rude selfish Bridezilla, or do I have a right to be in the spotlight alone?