Hmm, I resent the idea of putting someone on hold and giving them into 'safe-keeping' by another. To me, it totally devalues both the person who is to be put on the hold and their (not self-assigned) safe-keeper, who is seen as an intermediary thing to facilitate the progress of another relationship.
I don't see Vixen (hello Vixen, do join in whenever, we are a friendly bunch) being very realistic about this at all. While she has every right to not be poly if that is how she feels, then you are eventually looking into a mono/poly relationship, if you feel you are poly.
I think you should also get Red on the loop. It seems a bit unfair to be discussing her assigned role & function in your life and the future thereof when she probably still thinks she is developing a happily monogamous relationship with you!
Me: bi female in my twenties