I do not know exactly how to begin this story but let me give you some background. My mom died when I was born. My Father remarried to my step mom Kim. Kim never tried to be a disciplinarian just a really good friend. Kim is 35 and my dad is 45. Unfortunately he left us two years ago and Kim has become my legal guardian. She's a lawyer so there is no problem with money. Anyway my upbringing has always been very liberal and there has never been a problem with nudity in the home. Both Kim and I walk around naked. Kim has a stunning body she is 5'10' with 34 c breasts an athletic body with a small tight firm ass. I do occasionally get an erection around her and she has commented that its fine and that my girlfriends are lucky to get to play with my 8 inch penis.
The other day I came home early from school and was walking to my room when I saw Kim masturbating in the family room. She screamed and pulled a blanket over herself and apologized. I said it was cool and went to my room. The sight of her naked and pounding herself gave me a total hard on and I went to my room got naked and started to stroke my hard dick. Just then Kim walked in and said excuse me, we were both naked. Me sitting there with my dick in my hand. Kim asked me if she did that to me. I nodded and said yes and that she has gotten me like this. She said oh really, then I asked her if I could masturbate in front of her. She said she was not sure of this. I replied that we are not related so it does not matter. Her body was perfect and she sat down on my bed and watched me stroke my dick. This was the most exciting thing for me, I had never had a girl watch me masturbate. Kim herself then started rubbing herself and orgasmed three times. I was getting close and she asked if she could finish me off. I said of course and she began to stroke my dick harder and faster. It was amazing. While she stroked my cock I felt her pussy and fingered her and played with her breasts. When I came I shot 8 huge ropes of cum all over her and me, it was amazing.