Are my feelings ridiculous?

My mum has been seeing this guy for a year now. I've only met him 3 times for lunch. She's still married to my biological father, who does not know about her affair. Today she told me her boyfriend is coming with us to Las Vegas, and flying with us to drop me off at University. He wants to help move me in evidently. I'm a little upset because we're leaving in 5 days and she just now told me. She thinks I shouldn't be so angry about him coming with us on my last few days. Yes I'm 18 and my mother is an adult herself but we've always been close. Are my feelings of not letting him coming ridiculous?