Your girlfriend's little sister calls you up on video chat to say hi while she's away at college. Typically she only calls you when she needs something, and this time it's no exception; except she's calling to tell you that you should come visit her, alone, without your girlfriend. She tells you that she really doesn't think you two are a good match, and that she knows you're wanting and needing something different... her. Don't even try to deny it, she knows your cock swelled up the instant you opened the call and saw her there with her big tits busting out of her top. She convinces you to take out your raging hard on, encouraging you to stroke it for her. Taking her top and bra off incredibly slowly for you, she mentions that when she stayed with you and your girlfriend last month, she heard you whispering her name as you came thinking about her. That's how she knows all about your dirty fantasies about her. As you tug at your cock, she encourages you to jerk yourself to the thought of fucking her wild, and impregnating her - so filthy of you to cum to considering you're trying to start a family with her sister. Your gf's sister knows you want her instead though, considering how fertile and luscious she is. Playing with her tits for you and instructing you to fuck your hand, your cock is begging for release. She wants you to make a big mess with your cum, so she can see how much you want her. You're on the verge of exploding when she starts counting down, all while telling you she owns you now. She gets down to one and your cock oozes your seed all over your desk. You better clean that up quickly now, or else her sister, your girlfriend, will find out.