Talk honestly with your dad and listen to what he says. I don't know your dad, but I imagine him as a loving father who wants the best for his princess. Maybe he sees something in that guy that you can't see because love makes your eyes seeing blurry. Your dad is a man who has seen many things through his life and knows what could happen to you if you are with some kind of guys. Remember, your dad is there to take care of you and guide you. He is not there just because he wants to find a way to make your life miserable.