Shockingly, I have input on this. After my parents divorced my father married a younger woman who was my step-mother. She had a younger sister, who was technically my step-aunt. She was about 10 years older than me (I was around 20, she was 30). She was ridiculously hot. We used to chat all the time on AIM. Well one night we were both drinking and messaging and somehow that transitioned into sexting (or whatever sex-messaging is called). I lived out of town because I was in college, but shortly after summer break started and we started dating. I knew it would never go anywhere because it would be too weird for my dad and I to be married to sisters. But for a few months it was fantastic! The "break up" was pretty cordial. I went back to college and she didn't want to wait around for me which I understood. We had a few more messaging interactions after that but that's it.

As for the fallout, it's funny because although I know my Dad and his wife (her sister) knew about us dating, I'm not sure who else in the family knows. Nobody has ever mentioned it and it was about 15 years ago. We see each other at family events occasionally and it's fine. We are both married to other people. Awkward moment -- when my wife first met her, she immediately said "Oh my god she's gorgeous, imagine if you would have hooked up with your aunt ha ha."