Well my advice may not be what others here would give ... but here are my thoughts FWIW.
I understand that I'm a jealous person and that it's something that many poly couples have to deal with, but I refuse to accept a relationship with multiple men, I'm 100% sure that it wont work, and she's pretty stubborn about having the option available even though she's not currently interested in anyone else.
To me jealousy is one thing and this is ... something else. You have a line in the sand which is "no other men". She has been open and honest with you that there might (will?) be other men. IMO ... there is no fault or flaw here. I don't think either of you have been dishonest in your expectations or understandings ... it might just be that you're simply not compatible in this area.
Look, take it out of the realm of poly. I have a really good friend who fell in love with someone in college, but she knew from day one that she never wanted kids. Ever. Ever. And he did. And they loved each other very much, but ultimately decided that they simply weren't compatible in this area and broke up. Now, 20 years later they've both been with to other people for a while. He has 3 kids and a wife he adores. She is with a guy she's been with for the last 12 years and is extremely happy (they never married and don't want to). They each accepted that even though they loved each other, they weren't "right" for each other - or at the right place in their lives at that time.
To me your situation is much the same. Neither of you is "wrong". But you might not be right for each other.
So my personal advice would be that if you don't think you can live with this, you need to decide if it's a deal-breaker in the terms of the long term relationship. Same for her - if not being with other men is a deal-breaker, then is this a place to invest heart and soul in a long term relationship if you KNOW that there will be pain, hurt, and maybe even (probably) hurt feelings for both of you?
perhaps I should continue dating her in hopes that she doesnt find a new male partner that she's interested in during that time?
IMO this is a really bad idea. It would be like my friends above getting married with him saying "Maybe someday she'll change her mind about kids" and then getting angry, hurt, and upset when she didn't and it was too late to change things.
It's so hard for me because it took 20 years of life on this earth actively searching for that special someone until I finally met my first girlfriend. I had attractions towards women up until that point, none of which led to anything, but those were merely lust. My girlfriend is the first person for me to have fallen in deep love with.
While I appreciate and understand what you're saying, you are very young and it's very unlikely that this is the only woman you'll ever meet who you'll be in love with. I know that it's hard to see that when you're 20 and in real love for the first time in your life.
But honestly, the man who I thought was The One - who broke my heart in a million pieces, and who made me swear that I'd never love another the way I loved him when I was 26 - he wasn't The One.
I loved him passionately ... but there were other men who I loved equally, some more, some differently. It will be the same for you.
No matter what you choose, at some point you'll want to be able to look back on this relationship and have good feelings towards the woman you first loved with a real love. So, my opinion (and it is just one of many possibilities) is that you should part as friends while you can ... and while you still care about each other.