What should I do? please don't judge me?

If you value your friendship with your friend, you need to stay as far as possible from her dad. I know you said you are close to the family, but limit your contact with the dad. He probably has an idea of your feelings for him, and an affair would ruin your friendship with your friend and her relationship with her father. Try meeting more with her away from her home and keep as far as your can from her dad.