I agree with PPs about how giving up a fundamental part of yourself (or at least trying) is probably only going to delay the inevitable - that you won't be able to be monogamous, you and your girlfriend will both end up hurt, angry, and with broken hearts AND by then, there may be children that have come into this world and also have to deal with the fallout (assuming you're planning on having kids).
My first serious, grown-up boyfriend (the first one that we could sleep alone in a room together and my family wouldn't freak out about it) was nearly perfect for me, in every, single way but one. And by "perfect" mean that people in both his family and friend group and my family and friend group would say things to us like "seeing you together makes me realize that there is someone out there for everybody" (this was when I was monogamous). We were both quirky people, and just like each other in our very quirkiest ways.
So he was damn well near perfect. Except for one thing.
Our sex life was horrible. Horrible! Absolutely terrible physical chemistry. Soooooo bad. Every time we had sex was like that first time you have sex with someone new as a young adult and it's really awkward because you haven't had much sex and don't have confidence and it still feels weird to be totally naked and aroused in front of someone else. Every time. So bad.
Soooooooooooooooooo bad.
Given that this was my first serious relationship as a young adult, I didn't yet know how important sex was to me, and if this was a big deal (spoiler alert: sex is very important to me, and it did turn out to be a huge deal). And he was perfect in eeeeeeeeeeevery other way, so maybe I just needed to figure out how to cope with this sex this, because if I could *just* get over it, life with him would be perfect - wouldn't it?
(there was also this niggling little concern I had, in that I'd always been fundamentally wary of monogamy, in that I couldn't see how staying monogamous and only having sex and a close bond to one person for my Whole Freaking Life would really be satisfying, but hey, I figured that one out for myself in the end, so yay me)
Anyways, after trying for several years, and actually doing a fair amount of therapy over it, I learned that sex was extremely important to me, and that kinky sex in particular was something that I couldn't live without. Which was honestly a bit weird of a thing to realize, since I hadn't had any kinky sex yet in my life. But boy did I love kinky porn.
After a lot of painful agonizing, I realized that me and this guy just couldn't work. This was after years of trying to shoehorn myself into making this sexual incompatibly thing unimportant. I really hurt myself. I really hurt him too, as the longer we were together, the more he assumed that we were always going to be together and he was really happy with that idea, because we were so perfect for each other, except for that pesky sex thing.
(which he was aware was a problem on my end.)
So I broke up with him, and it was one of the most horrible things in the world. It took a whole weekend with a lot of sobbing coming from both of us, and misery, and him asking if I was *sure* that I couldn't just be OK with vanilla sex twice a month or so (which was about how often we had sex, though sometimes it was once a month).
The thing I remember the most was that at the end of that weekend, we laid down together to take a nap. We put our arms around each other. Our cats actually came up and book-ended us, so we were all cuddled together. I was in so much pain, I remember that I thought to myself that I wished we could just stop time there. I didn't want to die. But I wanted us to fall asleep for a hundred years and wake up with everything magically fixed. I wanted that so incredibly badly. Because he was so perfect for me, except for that one damn thing, and I didn't think I could ever find anybody else so wonderful.
To make the rest of this a shorter story, I will say that the following happened - he was so upset about the break up that he cut off all contact with me. I grieved enormously. I dated a number of people afterwards that didn't hold a candle to him. I worried that I'd made a mistake, especially since I'd not only lost our love relationship, but also our friendship.
In the end, when his heart healed, he contacted me, and we reconnected. Weirdly enough, a few months after we reconnected, I met Jon, my current partner, who is - if not THE love of my life - one of the great loves of my life. We're perfect for each other (including sexually!). And my ex is now one of my closest friends. We make wonderful, fabulous friends for each other.
Had I stayed with my ex, and stayed monogamous, I'd have been sexually unhappy my whole life, and not had the amazing relationship I have with Jon I also wouldn't have had a lot of other amazing poly relationships that I've had, and wouldn't give up for all the world. The closeness, the bonds there, the memories, the things I learned about me and helped others learn about them. None of that would exist.
My life would be poorer without those experiences.
If you stay with this woman, then you risk not finding a poly person (or even several poly people) who would be incredible for you. You cut down greatly on your ability to make loving connections with other people.
Yes, there is risk. Maybe you'll never meet someone as amazing as her. But maybe you will. Maybe you'll meet several people who are as amazing as her AND poly, so you can completely be yourself.
The last thing that I wanted to point out was that in your story, you mention that you have found and given up on two male loves in your life. From the sound of it, at least one of them (Guy 1) was poly too. So right there, maybe those could have been incredibly poly relationships that you gave up on, for a relationship where you can't entirely be yourself.
Why did you do that? Are you *sure* you want to live that way?
