I belong to a small art class where half a dozen of us - all men, get together and sketch various subjects ranging from landscapes to still life. We decided to advertise for a model to enable us to draw life pictures but where somewhat disappointed when the only reply we got was from a black twenty year old student called Michael. Nevertheless who hired this athletic young man who came to our class for a couple of weeks and we produced some good pictures of his well toned body which showed off his 9" flaccid prick. I told my girlfriend, Karen, who took a keen interest in the pictures and was sure that I had exagerrated the size of his member and was impressed by his physique. I kept the pictures in my portfolio together with all my other work which included various nude pictures of Karen. I suggested that she should pose for the group and not just me. We had been dogging on several occasions and she certainly wasn't shy about strangers seeing her ample 36DD boobs. She agreed and for the next two or three weeks she came to the class with me and was obviously very popular with all the other guys there. The following week, she again came with me but when we got there we found that Michael had also turned up. One of the other artists suggested that we could try our hand at erotica if the two models were willing to pose together. Michael had no problem with this and after a short chat and reassurance, Karen agreed to pose with him but insisted that she kept her thong on. It was decided that they should pose together with Michael laid on his back and Karen sat on top of him as though riding his cock. His hands were reaching up and cupping her ample breasts. It was very tasteful and very, very erotic. We started drawing and after the usual half hour we paused to give the models a break. Karen and Michael had been chatting to each other during the session and she had giggled at regular intervals. During the break, I asked her if she was OK with what was happening. She grinned and just said, "Mmmmmm." I asked what he'd said to make her giggle and she replied by saying that it wasn't what he'd said but was because he'd got an erection and she could feel his cock throbbing as she sat on it. I asked if it turned her on to which she said, "My thong is soaking wet. What do you think?" The next session commenced after our models resumed their pose and no sooner had they got into position, the giggling and smiling at each other started again. I was very turned on by girlfriend being excited by a young man's cock and was throbbing myself. During this second session, I could see that Michael's hands were subtly squeezing Karen's tits very slightly. I could see that her nipples were erect and that they both kept shifting about obviously caused by either being in some discomfort from his erection or by the excitement of her moving about to rub his erection against her wet cunt. This session lasted for another half hour and we again took a break to rest our models. During this break, I told Karen that she seemed to moving about more. I asked if the pose was uncomfortable. She told me that it was for him as his erect cock was trapped and she could not only feel it throbbing against her but could see it laid on his stomach. I said to her that perhaps she should take her thong off for the last session as it may be more comfortable and certainly more exciting. She didn't need asking twice and the final session started with both Karen and Michael completely naked. The giggles and movement started straight away and they were talking to each other. I can only assume what Michael said but Karen lited herself up and reached under her to hold Michael's cock which was at least 10" long and guided straight into her wet, slippery cunt and then resumed the pose. It was amazing to see. Neither of the moved at all. Karen has this amazing skill of controlling the muscles in her cunt and I knew that she was using these muscles to squeeze Michael's cock deep inside her. I could see by the look on both their faces and from the rate of their breathing that they were both close to cumming. It was a fantastic sight and such an erotic feeling knowing that she was fucking him without moving. His breathing suddenly got very fast and I could see that his cock was exploding inside her and shooting his cum deep into her. It seemed to last for ages before he finally calmed down and returned to normal. I looked around and most of the guys in the class had stopped drawing and were now standing there with erect cocks in their hands rubbing them off. The session had come to an end - at least from a drawing point of view but was to last much longer in other ways. To be continued