Later that night, after your girlfriend is gone for the weekend, you come into the living room to find her step-sister on the couch. She sweetly greets you and insists the two of you watch something together. You always like spending time around her so you don't see why not. Your girlfriend warned you not to fall for any of her supposed tricks, but what's the worst this sweet, smiling girl could possibly do? She chats with you and complains a bit about how harsh her step-sister can be, then she excitedly reaches for the remote so that you can pick something for the two of you to watch. Accidentally knocking the remote onto the ground, she bends over the sofa to get it and you get much more of a view than you were expecting. The sight of her panty-less makes you blush really hard. She takes notice and tells you how cute you are, you try to move on and forget about the fact that she isn't wearing panties. She continues excitedly talking your ear off, sitting in various positions that keep you thinking about what she has on, or doesn't have on, under her dress. The conversation starts to take a bit of a turn when she begins asking you questions about you and her step-sister's relationship. You try to brush it off but you can't help indulging her a bit. Some awkward tension starts to build, but is quickly cut short when she tells you that she will be back in about 20 minutes.
Your girlfriend's step-sister returns wearing lingerie, covered by a sexy little robe. You ask her what she thinks she's doing but she insists that she isn't crossing any boundaries. She proceeds to tease you, taking her robe off a little at a time, and posing in various ways on the couch infront of you. She tells you that teasing isn't cheating, even touching isn't cheating. There are so many ways she could touch you that would never be considered infidelity. She starts rubbing her pussy, telling you that watching eachother masturbate isn't cheating either. Why should the two of you not just enjoy this? It's not like her step-sister will ever find out about it anyways, and after all, she is the prettier and the nicer step-sister. You know better but you can't help it, you take your cock out and stroke while she touches herself. She climbs on your lap and starts grinding her pussy up and down your cock, insisting once again that this isn't cheating, it would only be cheating if you actually go inside of her.
She takes matters into her own hands and puts your cock in her pussy, but just the tip. That isn't enough and before you have time to consider what's happening she is riding you and you are full-on fucking. She fucks you until she cums. She turns around and fucks you in reverse, begging for you to cum for her, over and over again. You can't help it and you blow your load deep inside of her, she relishes in it and won't let you pull out your cock. It makes you stay hard. She turns to face you and starts fucking you again, while she tells you that she should be the one you're with, and insulting her step-sister, your girlfriend, repeatedly. You both cum again, somehow you manage another load and let it blow deep inside of your girlfriend's step-sister.
