NOTE: This post was too long. I tried to shorten it a few times but it remained too long, so I'm dividing it into two posts.
I think that I share many of the same urges, feelings, and desires as a poly individual, but I don't share the same social rules. To me, it's very easy to simply not act on these urges.
[...]The majority of modern (American) civilization [...] act on these impulses (the same ones I have.
Being a responsible monogamous individual involves not acting on these urges.[...] I deal with it every day, and I don't act on my urges, so what makes it fair for my partner to be able to have other partners, while I sit here being "responsible" and not having other partners?
I find it very interesting that you think of these feelings as urges or impulses to be resisted. You praise resisting them as being responsible and good. And it sounds like it's some kind of sacrifice too, that you do for your partner. Considering your partner is poly, she probably doesn't appreciate it the way you think she might. I personally equate it with something like flagellation, and I would hate for my partner to make himself suffer and, worst of all, say it's all "for me" (which would make me feel like it's my fault).
If I have a friend, I might find other people nice and want to become friends with them. I might invite them to a movie or a museum or any other activity. Why isn't that feeling of wanting to get close an "urge" to be resisted, as well? To me, it's the same thing.
And if I had a friend who insisted on having no other friend and did his or her best to prevent me from having any other, frankly, I would be very scared by them. I'd think they have some psychological problem.
Not saying monos have one, simply stating the way things look from here. Monogamy is the social norm, as you have pointed out, so I am very familiar with it. As a result, I feel polys have a much easier time understanding where monos are coming from, because they've witnessed the reasoning all of their lives and are used to it. They're so used to it they frequently wonder if they're a terrible person for being different.
What I want to do is try to explain being poly, from my point of view and experience, to a mono, as I realise it's harder for you to grasp because you have much less examples of it and explanations of how it works.
For me, I don't throw anything out of the window when I start a relationship with another partner, and refraining from other relationships doesn't make the one I have more sacred or important. Not only do I disrespect other people by telling them "you weren't there first so you're q less important human being", I'm also, in my opinion, disrespecting my first partner by telling them the relationship needs to be the only one in order to be special and sacred. I'm also disrespecting myself by refusing to let myself reach out to people who have touched me in a special way.
For me, having several partners makes it more obvious that I love them all, because it's never "if I left you I'd be all alone, so you might think that's why I stay with you". It's always "I'm with you because I love you. Look, I don't depend on you, therefore I'm with you on my own free will."
I understand that you think dependence is a proof of love. "I'm making myself so vulnerable that without you I have nothing, therefore proving I want to stay with you forever". Well to me, being dependent on me places huge amounts of pressure on my shoulders never to be sick, to get into an accident, or to die. It means that anything that happens to me, I can't relax and try to get better because I'm too stressed out about how it affects other people.
For me, it's a stronger proof of love to say "if something happens to you, I'll be devastated. But I'll survive, so relax and take care of yourself, and don't worry about me". It values the other person's independence and individuality.
I find the idea of being devoted to a single individual and living a long life together as best friends to be a very attractive method of living. My partner is my rock, my island, in a sea of chaos, and I am hers. That's romantic to me.
And that's your right! Just like it's my right to have a different vision. And I can understand to some extent, as I said, I was raised in the same society you were. I see it everywhere. I just feel differently. You partner feels differently. At that point, you're both faced with a choice: do you find someone who sees things the same way you do, or do you say "being with you is more important to me"? That's your call. But I wanted to show you that as much as you see it as you compromising your vision, you need to ask yourself is she is compromising hers. I would be if I was with a mono, even if he "let" me have other partners.
I would feel like I have to give him more of my attention than to my other partners, which feels unfair to other people I love. I would feel pressured, being his only source of sex and romantic affection, to perform more and better. I would feel guilty if he is ever in the mood and I'm not, because I would know he's not getting any outside of me, and therefore I'm not just saying "I'm not going to have sex", I would be saying "you're not going to have sex", and I don't like feeling like I'm controlling someone else's actions.
With a poly person, even one with no other partners, there is always the potential for them to get it elsewhere if they want it or need it, so I don't have to worry about their "sexual maintenance", they can do it on their own, know when they need more of it, and get it. With a mono, I have to monitor it too because I'm their only source, and it wouldn't be something I do for me anymore, it would be something I would do for them, because if I didn't I would feel like I'm denying them something major.
If I have poly partners, I only need to worry about my agenda, life, sex life, and so on. If I have a mono partner, I have to worry about theirs too. In a way, I feel like their keeper. I understand fully that it's not true, but still, by saying "there is only you, nobody else" I really feel like they're saying "I'm putting all the responsibility of my happiness on your shoulders alone".
It's daunting for a poly person like me who isn't used to that kind of thing. It feels like the tiniest slip can destroy the person you love and cause them immense pain. I don't think most poly people are as comfortable with mono partners as they are with poly ones. To me, it's not "a mono partner is easy and a poly partner is hard, so in mono/poly relationships the mono partner gets the short hand!". For me it's more "monos know to deal with mono partners better, and polys know to deal with poly partners better, so mono/poly relationships are very challenging on both ends".
I can understand why it would be more challenging, generally, for the mono partner. As I said, we polys have the "advantage" of being in a mono society with mono conditioning. Even if we can't relate to it, we know about it, we grasp the concept, we know how it works. We started being conditioned from an early age, when you have to start when your partner comes out. And it must be very hard when you didn't know such a thing as poly existed, and you feel they threw in onto you when you didn't ask for it. But I don't think it is unfair, even if I understand how it would feel from your point of you. From the poly partner's point of view, they've had to "play mono" all their life up to that point, and they want to be able to be themselves, just like their partner can, finally.