Honnestly, peoples who ship polygems are the ones who got it all figured it out.

Honestly, "three is a crowd" seemed to me more like an excuse to send Jamie away than anything. If someone is shipping, for example, Pearlnet, it means they are shipping Pearl and Garnet, not Pearl and Ruby and Sapphire. Garnet is more than just a sum of Ruby and Sapphire, she's her own character with her own personality and tastes. In a way, Garnet can be viewed as Ruby's and Sapphire's "child". Your parents once fell in love, and you are the product of that love, but you are also your own person and can have your own love interest. I know, this analogy isn't exactly accurate, but still.