For a very long time now my best mate and I have been fairly open with chatting about porn, girls, and fantasies we have, usually getting to a point where we start jerking off to whatever we are talking about together. Ever since we started doing it he's been very open about his fantasies of fucking my twin's huge tits, and was kinda surprised at first when I agreed with just about every fantasy he had of her, and started telling him all the equally dirty things I'd wanted to do to her myself. Sometimes we would spend entire sessions just looking at pictures of her in bikinis and her stretched crop tops and talking about her and it always felt incredible because of the taboo

About 3 weeks ago my mates younger sister turned 18. We were stroking off to my own sister yesterday evening and I'd told myself I wasn't going to bring up the subject, but once we were going at it I finally asked how much he'd been thinking about his own hot little sister since her birthday and he immediately started throbbing harder. He said he'd been waiting for me to bring her up and it felt so good stroking together telling each other about what we'd do to each others sexy siblings now that the fantasies can go both ways. We ended up pulling up a birthday pic of his sister and came probably the hardest we have in years over his sister for the first time. I have a feeling that now both our sisters are fair game for fantasy our sessions are going to have a whole new dynamic to them