"You promised that you would do whatever Sandy asked to keep her happy, remember?" Melanie says.
Yes, but you protest that doing that shouldn't involve violating fundamental standards of morality.
"But it's only you who can violate your own standards of morality, not Sandy," Melanie replies. "If Sandy wants to be fucked, you should fuck her. And if your principles don't allow you to cum when you do that, then you'll just have to hold back! See, you just have to be strong, even though you are obeying her!"
You protest that Sandy might order you to cum inside her...