This happened when I was thirteen. Belinda's family and mine were close. We had known each other since we were three.
Belinda's family and mine were very close to one another, and often travelled together when we were children. She and I were the same age. On trips it wasn't unusual for us to be bathed together or to swim in our parents' pools together in the nude until we reached about the age of ten. After that we still travelled, swam, played tennis and that sort of thing together, but neither of us ever thought of the other as a sex object, although both of us were well aware of the other's growing sexuality.
Until one Saturday. I was home alone when to my surprise, Belinda arrived. Of course I invited her to come in, offered her a cola, made small talk and the like. She seemed preoccupied, so I asked her if something was wrong. She smiled and asked if I ever got horny. I answered that I was always horny. She moved closer and planted a big kiss on my lips. We began kissing fiercely, and I began to feel her little size B tits. She began to breathe heavily, and so did I. I took her by the hand and we walked to my room. We continued our making out, and I sat down on the bed with her next to me, opened her blouse, slid her bra up, and got a clear view of her tits. They were little cones topped by reddish aroleas surprisingly large with eraser type nipples which were hard to my touch.
She wasn't idle, she had a firm grip on my pulsating dick which she released to open my fly, reach in and grab the now aching hard thing. I got her blouse and bra completely off, and began to rub her vulva from the outside of her panties. She said to wait a minute as she removed her clothes; then told me to do the same. I did, and we lay back on the bed, and kept stroking our genitals. I put first one finger in her pussy, then a second and a third. While I was doing this she was stroking my now rock hard purple headed oozing peter.
She stopped for a minute, took my hand, and said that she wanted what I later learned was her clit stroked in little circles with two fingers keeping her clit between the fingers. A minute of this was enough to get over the cliff. When she began to orgasm, I first felt a flow of fluid, next she began gasping, her body stiffened, and I felt what I knew was the contractions of an orgasm, having had many of my own by that time. She squeezed my dick so hard while she came that it hurt. When she came down from her high, she told me to lie back, and began to fiercely jack me off. I soon shot the biggest load ever to that time getting it all over both of us. Then she snuggled next to me, and we began to talk, asking each other if this was the first time we did this with a girl or boy. It was. I asked her if she knew I was home alone. She said yes; that my mother asked her's to keep an eye on me, but she did not intend to do anything other than to invite me to supper. So Belinda knew the coast was clear for several hours. This was the beginning of a teenage love affair that lasted for several years.