I am sorry it went down the way it did, but I can see where it would be very difficult to navigate different relationship styles, much less a broken trust issue long distance.
We often speak of people being mono or poly, but that said, the truth is the tendencies probably lie along a spectrum. For example mono couples often will have sexual threesomes. Not exactly full blown poly, but hardly steadfast mono either. So I agree, while the concept of full blown poly is foreign to you, you do seem remarkably open to the concept.
I hope you are doing all right.