Agreed, agreed. You have met a woman who is confident and open to what she wants and willing to explore that. The relationship is too new to start talking 'primaries'/'secondaries' - they belong more to the 'married with kids' world.
Bisexuality isn't easy from the viewpoint of a monosexual partner, and much less so in poly situations. Are you more threatened by thinking Andrea will develop a deeper connection with this Chris guy, or that she will want to pursue a relationship with her BFF independent of you? I am super-sceptical of FMF triads, so maybe that colors my viewpoint overly much, but really, she is her own woman and you have the opportunity to cherish that.
If the problem is that you are no longer talking with Andrea, that's a whole other issue and much easier to solve.
Me: bi female in my twenties