Try and remember that this just happened and that there is a WORLD of things to learn. I find it encouraging that you are already seeing how it might work for you. Good for you. Even if you decide it doesn't, it is at least a start to wrapping your head around what she is asking for. I would be careful to not use that as a way of evening up the score somehow or competing with her though. Women find far more men so you will never win...
at least that is what it seems to be like.
Everyone has offered some great advice, you have a lot of work to do and it would be great if your girlfriend agreed to doing some of it with you... at least listen to what you have discovered and read that interests you about your situation and others.
It sounds like you are on top of your feelings so far, sad, confused,... crazy. All right on the money of what others have said when they have been in your position. And oh there have been many. Keep at it, you are young and as you say, have lots to learn... all in good time and as it should come to you. So much to explore... I'm actually gleeful for you
Maybe because poly was exactly what I needed at your age and it didn't exist! Oh the cheating I would of avoided... okay, now feeling jealous.