Do you like your parent's new partner? why or why not?

I don't like my dad's girlfriend too much. I mean she is a kind respect woman but she isn't my mother! My dad did warn us we'll be seeing a LOT of her. My mom died when I was 18. My dad was devastated. Six months later guess what...he starts dating a new woman. I can't believe he moved on so fast. They've been dating for three years. Just celebrated their 3rd year anniversary. My friends are suprised that my dad hasn't popped the question yet. My dad's girlfriend even said she would never replace my mom and always think about the good times. I love her for that but still don't LOVE her like family. My dad said I need to move on from the past and my mom isn't coming back. She would want me to move on and find happiness. I was very rude and nasty towards his girlfriend at first. My dad called me out on it and said to stop being a jerk to her and back off of him. I didn't understand why my dad was hard on me since my mom died.