Forbidden Sex with my Sister's Girlfriend

There are some things in life it's probably not a good thing to do, one of those is to have sex with your sister's best girl friend. It is not only a taboo thing to do, but it also leads to so many problems it's not worth it. I knew all this. Which is why one night I threw all my experience out the window and slept with my sister's best girlfriend. Why not be a voyeur, and see what happened!