Age is really 17, my older sister is 18. I have a fucked up situation. I've been dating my gf for two years now, never had sex, she wants to wait till we grad high school. Cool.
My sister is a beautiful woman who is a closeted slut, total party girl. I've heard the stories and seen a few pics of my sister have sex with other girls, occasionally I hear a story about her having sex with guys. When I've asked her in the past she says she usually has sex with women because it's bigger and everytine she hooks up with a guy it's bad because they usually smaller dicks. Cool, my sister wants to stay with women, great, no getting pregnant.
Recently though, we went on a camping trip with a few friends from out of town, we'd gone up to a place A little ways from Asheville and we're having a great time. My sister and I decide to only take one tent because we didn't want to carry a bunch of crap. Our third night out there being as close as we were and with our friends we got down to skinny dipping and washing in the river. Great eye candy for all. I never thought anything of it. That night our friends had bought a significant amount of alcohol and we enjoyed in our riches and Mother Nature. We played games and told dirty secrets of our lives. Eventually it came time to crash out, and all was well. My sister though and her amazing body had been burnt in my mind and I couldn't stop thinking about seeing her naked, with such a firm round ass, perky "B" cup tits with thick nipples that were pierced.
Shortly after falling asleep my sister woke me saying she was freezing cold and asked if we could share a sleeping bag to which I shrugged off with a yes and attempted to go back to sleep. As she got in my bag I was only wearing my boxers and I could feel her smooth skin run against my body, and only felt that she was wearing a thong. Her nipples pressed into my back and I began to have an erection. It was quite and still for a few moments and then she began to kiss and nibble on my neck and ear. Her hands began to wander and I felt her grab and squeeze my ass, and grab ahold of my hard cock the best she could to which she quietly blurted out "ouch, that would do some damage." I tried to deter the situation, poorly I must say, but so we were passionately making out. Without hesitation my intoxicated sister position my wife cock against her lips and forcefully pushed me into that wet pussy, she painfully moaned and cried a little saying that I had stretch her pussy unlike she had ever felt. It was great and horrible at the same time. My sister rode me like a stallion, panting heavily and burning up like a nuclear bomb. She reached her climax on top of me and gushed like a waterfall over me. She fell on my chest gasping for air and kissing me wildly. We had sex two more times before the sun came up, the second time I got my climax and she swallowed me down and the last time we had anal and I cummed inside of her.
The next day everything went back to normal like nothing had ever happened. We returned home and my sister changed everything she was. She stopped partying, stopped sleeping around, she actually improved her grades.
The problem comes in at I still am in a relationship wit my long standing gf. My sister though acts like we are in a relationship. Texting me all the time, doing sweet things for me, wanting sex from me all the time, which we do but now it's like she wants us to get caught and everyone to know. Being siblings we grew up saying we love each other but now she says it in a new light. My sister literally wants me to her own. It's getting crazy now. I tried to break it off but she says she'll expose everything so now it's turned into blackmail. We fuck whenever she wants and she so loud, moaning, screaming, crying when I slam her too hard. I just don't know what to do. Should I break off my gf or just let my sister out us? I just don't know