Keep your friendship intact by following these guidelines to dating your friend's sister. When the attraction is mutual and a dating relationship develops, there are some guidelines that should be followed in order to keep the original friendship intact. Insist on remaining neutral and not being brought into the middle of the argument. It is a no-win situation for you, should you voice any opinion at all. Keep your lips sealed tight. Stay on good terms: This would not be a good time to get your friend upset with you. He has the ear of your girl, and he could do irreparable harm to your relationship with her, if he was inclined to do so.