I guess the difference for me is my fear was generated from the unknown of possible other new
Lovers that may replace me as the "new guy".
I was not afraid to be cast aside by those already involved. I would step aside if they asked me to or if I thought I was hurting Redpepper's primary relationship with her husband.
My happiness in our polyamorous relationship is dependant on the well being of Redpepper and her family as well as in the immense love and passion we have. If thier happiness required me to not being an intimate person in Redpepper's life, I would gracefully reshape and re-direct my love for her but still be a part of thier lives if they wanted. She would still be my most trusted friend. This is not an indication of a "lack" of love, but an indication of the overwhelming extent of love I have for her.
Security does indeed come from inside to a great extent. But always tell your partners what you are feeling. It is a process that most will experience. You are not alone