Yikes! That is a slippery slope...I mean how much control should a primary have in the choice of secondary for one in a V situation? I don't think I would be one for giving that kind of cart blanche.
Then again it all depends on what kind of poly life you all will be leading. How much interaction amongst friends and family etc. Why does your primary feel threatened by this secondary? Is it the very common territorial thing or is there a real reason for distrust? Can't offer much advice but I can offer to be someone who listens to your issues. Best of luck.