My sister and I would often sexually "play" [when young], which usually did not involve penetration or anything more than just kind of rubbing up against each other while naked. We did this until probably the age of [she was a year younger than me] when I moved in with our dad and she stayed with our mom.
[Later...] Since I was already sexually active at that age with an older girlfriend [a couple of years older] we went a lot further, including me performing oral sex on her. Eventually we went all the way, with sexual intercourse that lasted at least an hour. She was very willing in all this, and though we started with me on top she later told me she wanted to switch positions. She seemed fascinated when I [ejaculated] on her belly. For days afterward while she was still visiting at our dad's place she kept asking me about [ejaculating], what it felt like and did I shoot more if it felt better. Eventually this led to her performing oral sex on me to the point of orgasm...
We had sex one other time, [a couple of years later], that time at our mother's house. Well, I guess it was twice, but both times on the same afternoon where we had the house to ourselves.
We visited more often than we had sex, it was just something we did occasionally, usually when my sister gave me some indication that she was feeling really horny for whatever reason. The relationship never changed much else about the way we interacted. It never seemed like something that bothered her, and I never felt like I was dominating her or anything. She's a very strong-willed girl, and always has been.
This is where is gets a little crazy, and some people will call BS, but I swear it happened.
I've only told a couple of people about our experiences, but I did tell one girlfriend, who just came right out and asked me if I'd ever f---ed my sister (she could tell we were unusually open with each other.) I admitted we had and gave her the details, and she got really into it, rp-ing in bed as if she were my sister. It was a little weird, but I went with it...
On one night, we ended up hanging out with my sister [when we were all adults]. We smoked a little pot and had a bit to drink, and then my gf left the room for a few minutes. When she came back my sister and I were making out, and she just jumped right in. (I know, I know, but it happened! It's a crazy world we live in.)
We ended up in a big threesome that lasted most of the night. I had full intercourse with my sister again, with my gf guiding the process and asking my sister if it felt good.
The mistake here was that I thought my sister was on the pill and I [ejaculated] inside her. She wasn't. She didn't get pregnant or anything, but it really scared her. Enough that on the only other time we wound up naked in bed together, when we were both in our early twenties, she decided she didn't want to go through with it. We had oral sex instead.
It's been 17 or 18 years since that night. My sister and I are both married (not to each other, lol) and she actually acted as the officiant for my wedding. Both of us have kids, jobs, etc. We've both been fairly successful in our lives. My wife has no idea about our history, nor does my brother-in-law. My wife has remarked on how open my sister and I are with each other, and how it's a little weird, but at this point she and I live five hours apart so we see each other pretty rarely.
Honestly, I'd love to have sex with my sister again. Even at 39, she's still a very attractive woman. I don't know if she'd still be interested. I suspect not, but the situation just isn't going to come up, unfortunately. We're basically never alone together.
I think incest like this is probably really common. I don't know of any other brother-sister couples, but I did have an old gf tell me about some early sexual experiences with her father that didn't seem to traumatize her to badly.
Another girl I dated with "daddy issues" didn't really know her father, but when she and I were seeing each other I was 16 years her senior. She used to call me "daddy" whenever we were alone, and late at night when we were in bed together we spun this elaborate mythology about each other, and how she was actually my daughter and how I'd made her out of my dreams. It's was weird stuff, and very intense. It concerned me a little, since this was a girl who was a bit off her rocker and she was still in high school when we'd met (over 18 though.) Eventually we split up but the last I heard she was acting as a sugar baby to some guy even older than I am. Honestly, I'd bet she is very happy in that relationship.
It's just a big, crazy world, with a lot of different kinds of people. So many people have these private lives where they do or fantasize about all kinds of things that society wouldn't approve of. My feeling is that the less we judge others, the more free we ourselves become.
Thanks for putting this page together, and to everyone who has commented thus far.
I don't think his experiences like his are extremely rare. If you've had similar experiences or are aware of someone who has, you are welcome to contact me.