My mom started dating

My dad died 4/27/22 and my mom starting dating a guy she knew in high school recently. I want my mom to be happy but I have very complicated feelings about this. She started telling me about her date like it was no big deal and was just a normal every day thing. I miss my dad every day and I don't want some random man coming into our life. My mom was talking about he hasn't been married and doesn't have kids so she's bringing a whole family to the table for him, grandkids and all. She said it so off handed. Like I know they aren't that serious yet but I'm an adult, I don't need a new dad and my son doesn't need a new grandpa, he already had the best one.