Stepsis got home from a party at the morning. She told her stepdad she will take care of him with her mouth so he doesnt tell her stepmom

My ex girlfriend's 18yr daughter got in trouble at school one day and called me to come get her.when we got home she begged me not to tell her mom when she got home.she came out of her room wearing a sexy little gstring and tshirt and said"I know how much you like my ass,if you don't tell you can rub on it and jerk off to it"that day we started making deals whenever she wanted something.