I quickly read over all the post, but does the stepsisters get along???
Now if she dont, why not get her to tell your ex that she has been sleeping with your ex-bestfriend and that she missed her period?
Two birds, one stone.
And yes you should use a rubber if you do.
And I feel the reason that you dont want to follow through with it, is because you dont want to hurt your ex. I'm not dogging you, I felt the same way before I messed around with my ex's friend //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif