LW1, you are a predator and need to walk out of this family's life forever. You have been lusting after this kid since she was basically a little girl. You've manipulated her and groomed her. You will ruin her relationship with her mother forever if you sleep with her. What happens when she hits 25 and starts to lose her youthful appearance? Wait another 7 years until her then-daughter turns 18 so you can abuse her too? Gross. Get away.