You tell brother that if you're going to have sex again that he has to wear a condom, but then when brother is ready to cum you tell him to take off the condom and keep fucking you and then say that it felt so good before it's OK if he cums inside you again. But you tell him that if you both are going to keep doing this then you are going to have to get on some kind of birth control. After he cums inside you, have him pull out so that the creampie is visible, but then have him insert his penis back in you and you continue to have sex for a few more seconds.