I was thinking of two story ideas. They are pretty much the same but the roles reversed. Which idea do you think would be better?
Guy finds out that his girlfriend has been cheating on him because for some reason she thought he had a small penis. He had walked in on her and her lover and the lover did in c fact have a bigger penis. She sees him and tries to explain why she cheated, she thinks he's about to calm down or about to leave when she accidentally says she had found out he was going to propose and she wanted to get having sex with big cocks out of her system. Without thinking he says she'd be very surprised with his size. Then he storms off. He knows someone who was working on an experiment that could enlarge his penis much bigger that very day. It works and he goes back to his girlfriend and she's surprised he came back and actually had a big dick. After the sex he eventually finds out the experiment had some side effects. He needs sex often and he can't help himself around other women. His girlfriend could catch him with her sister or his sister, and thinks it's only fair since she had sex with that guy he caught her with and some guys he didn't even know about. But he might not stop there with the sister. Some girls end up pregnant.
For the alternate story girl finds out her boyfriend is going to propose to her and she's afraid that once they get married he'll be mad once he finds out her pussy isn't very tight. She told him she was a virgin or had only had sex once a long time ago with a small diced guy. She says she doesn't believe in sexual toys for the pussy. So she goes to someone who can tighten her pussy and regrow her hymen. She doesn't know of any other way. After she has sex with her boyfriend after he proposes she finds out her sex drive is out of control. She gets caught by her man doing it with either his or her brother or even both at the same time. She may do it with other guys too. But her guy probably won't find out about them. She freaks out over the fact that not only does her vagina and hymen always return to the condition of a virgin after not having sex for a time but she also finds out she's pregnant.