First Time to Shoot Off

I often spent the weekend with my Grandmother. Her house was always filled with various relatives, but my Aunt Billie lived there all the time. Billie was a little on the voluptuous side, with big tits that were always braless and a round plump ass. I had been masturbating, often thinking of her, for about a year, but my first orgasms were dry. This particular weekend, the house was full of family members, so sleeping space was limited. Aunt Billie suggested that I sleep in her room, rather than on a sofa or in a sleeping bag. When we went to bed, she pulled off her jeans and got into bed with just her panties and a t-shirt. I always slept in the nude at home, but out of shyness or decency, I kept on my briefs, only. The night was actually rather cold for our southern climate, so I found myself snuggling up to Billie to stay warm. She took my hand and placed it directly under her breasts and scooted over so that her butt was directly against my crotch. She soon began snoring, but my young penis was pressed snugly between her ass cheeks. My penis was maybe five to six inches long at most, but I had always had a large cock head. The more I thought about her butt being separated from my cock by her nylon panties and my cotton briefs, the harder I got. I was too afraid to move against her butt very much, because we were good friends and had never had any hint of sexual contact with each other in our whole lives. Without appearing to wake up or being conscious of what she was doing, she adjusted her sleeping position so that now the head of my cock was actually poking into her panties, between her ass cheeks. The stimulation was almost too much for a horny teenager, so I slowly began to hump against her butt. Whether she was really asleep or not, I did not know, but she seemed to push back against me, meeting my gentle pushes against her ass. Now the head of my cock felt the crack of her butt, even though we had two layers of underwear between us. I realized that I actually might orgasm, but rather than her pull back, she increased the pressure and speed of her movement against my cock. Suddenly, I felt my orgasm was inevitable, and I drove my cock as deeply along her ass as possible. Then something wonderful happened! I felt my sperm shoot for the first time. Despite that we were both wearing our underwear, I am quite sure that the amount of wetness would be noticed by Aunt Billie, but I could not stop! I came like a porn star and my orgasm lasted what seemed forever. Then I could tell Billie was breathing heavily herself. She took my hand and put it under her panties and used my hand to masturbate herself to what I later found out was a female orgasm. I could feel her wetness and even her huge, swollen clit. I am sure that I was probably not doing exactly what she needed to get off, but she placed my hand and used it with her help. Nothing was ever said between us about what had happened, but when I awoke in the early morning, she was stroking my cock slowly, right behind the head. When she realized that I was awake she increased the speed, until her hand was almost a blur. I ejaculated almost immediately. Again, nothing was said between us, and we went back to sleep. Later that same morning, something even more incredible happened, but the rules of this site will not let me describe it.