Well, see, the problem here is that, as you've said in your other post, you've identified something that you think might assuage your feelings of insecurity, and that's to meet your partner's partner. How can you know whether you're cut out for poly, when your first foray into it is happening in such a way that you're not being provided with the thing you think you need to be ok with it?
It really is ok to need to meet your metamours in order to feel comfortable. If you meet your metamour, everything is on the up and up, and yet you're still feeling uncontrollably insecure, then you'll know that poly isn't a workable option for you.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.