Thanks for replying. I agree that it isn't fair to wait until in a commited mono relationship to bring it up. I think I kind of meant "Tell them it's a possibility" VS "Tell them when it happens" ... I think being upfront in the early stages as you said is the most sensible approach.
It's funny about the friends. They've stuck by me through thick and thin and their three of the most amazing people i've ever met. One of them I think would understand as her own father still to this day says that he loved her mother and his wife equally and she now says sometimes that she understands. The other two have been cheated on by abusive boyfriends who had affairs and I think in their minds Poly is basically the same thing which it is OBVIOUSLY NOT. These friends have never actually met my Poly friends, they judge them based on what they've heard of them which is a real shame!!
Thanks for replying and giving good, sage advice! Really helps to clarify my own thoughts.