"Yes, hasn't she told you that's her ambition? You must be a very lucky guy to be her boyfriend. She tells me she absolutely loves the thought of having a cock inside her pussy and fucking her! She even wrote on her application that she craves a man's cum!"
You are flabbergasted. You say that Sandy is just a good friend who is helping you out. You tell Melanie that Sandy is not your *girlfriend* by any means. And you say that you and Sandy have never even kissed, let alone made love.
However, in the back of your mind, you are not very surprised. Sandy has always been an absolute tease and she loves to tease you by talking about sex. Indeed, Sandy has asked you to make love to her many times, 'just as a friend,' but you've always managed to avoid it, so far.