My girlfriend and I have chosen you to donate semen to us. I want to milk you for your semen so I can impregnate her and myself later. You don't have to do anything, you just have to lay there while I ride you to get the most amount of semen. At the moment your going to cum I'm going to jump off and pump all your semen into a cup for us. WELL... that was the plan anyway, we didn't take into account that I really love riding your cock. So why not just impregnate me anyway?