my Stepsister and I used to masturbate together periodically off and on for about a year while in early high school then for some reason we just stopped doing it. I think we were just both curious at that time. It's been over 30 years ago but the thing I will always remember most about it was how horny she got when I would cum and she would make herself climax almost immediately after watching it. Other than me rubbing her legs we never touched each other but now I fantasize about what I could have done with her but I was too shy and didn't know very much at all what to do with a girl at that age.