How do I say NO!

9 weeks pregnant and my father just announced that he's getting married on mine and my SO's 6 year anniversary. This will be his 3rd marriage... is it wrong for me to feel EXTREMELY upset about this? And then how do I tell someone who doesn't care about anyone except himself and he can do what ever the hell he wants to because no one else is important that I don't want him getting married that day. I'm at the point where I don't even want to go and he's booked his wedding 8 hours away from where he was raised, grew up, and had a life with his kids for the last 20 years. Am I being overly hormonal and emotional? Or am I right to be mad about the date.