Dang Rusty beat me to it!
He makes a lot of good points. In my personal experience I guess I would have been the 'primary' as my wife and I had been together almost 2 years prior to opening up our relationship. When she started dating her boyfriend to ensure she didn't disappear in a puff of NRE (new relationship energy) we had clear guidelines...as her relationship with her boyfriend progressed we moved away from the primary/secondary idea to one of equality with all involved voicing what their needs were in terms of time, intimacy, etc.
Again it goes back to communication, and like Rusty said, it's about accepting your own self worth in the relationship while understanding that their is a third person with their own needs that you need to respect as well.
Polyamory is wrong! It's Multiamory or Polyphilia. Mixing Greek and Latin roots? That's wrong.