Homewrecking seductive Stepsister made me cheat

I really wasn't looking forward to getting together with my family for my Stepdad's birthday. My Stepsister is always the highlight to these get togethers. We don't see each other too often but we were always close. We had a lot of fun together back in the day, sometimes we crossed the line. When I offered to pick her up I wasn't expecting her to quiz me about my new girlfriend. I wasn't hiding it from her as such but I know what she's like. She likes to tease, I'm sure she gets jealous and wants to see if she can still have me. Of course she did. When she asked me to pull over I knew what would happen. I tried to resist. Watching her smoking, hitching up her dress and pissing right there in front of me. I was hard and she knew it. Spreading her legs right there in my car and stroking her hairy pussy, begging me to lick her clit. I should have used a condom but she wanted my cock raw. Wanted me to creampie her. The thought of her sitting there with the family dribbling my cum!