Thanks for the response peabean. I haven't ever been part of a triad but I've definitely felt a sense of "tolerance" towards my intimate partner when she experiments with people I don't know. I'm not sure what it is... if I don't know the third person then my energy kind of shifts from an open appreciation of the known to a closed toleration of the unknown; I'm not quite resentful, just a bit uneasy. I would almost rather not know if she's seeing someone else just to dodge my own feelings. Not knowing the unknown, you know?
This is probably a kind of growing pain but I feel like it's not an uncommon one.
I'm wondering how this might change in a triad since everyone is in the loop - everything is known, and there aren't any known unknowns, if you will.
I should tell you that my understanding of a triad is three people who love each other in a "closed loop" - polyfidelity.
Much of it is that my girlfriend often feels we would 'be better off without her' and she worries that we don't need her.
Is your situation closed loop, or are you all open to each other seeing other partners?