(Breaking the rules on version reading, but I read the other one first, and this one has more relevant discussion.)
The OP almost made me cry because of my current romantic situation. This comment didn't help (I mean that in a good way). I realized during my first (and so far, only major) romantic relationship in college that while there was enormous value for me in having such a relationship, I couldn't stand the exclusivity. I said so and it didn't go over particularly well, but I continued trying to compromise. Our relationship was on-and-off in college. Now we've graduated and live in different cities but for over six months until recently had a happy open relationship (or sexual friendship, or whatever you want to call it), in which we visit when we can and talk by phone the rest of the time (we're both busy grad students comfortable with low communication frequency and high average conversation quality). As of the beginning of the summer I was trying to start a romance with someone at my current university. We hit it off right away after meeting each other, and there was no question about chemistry. Things seemed to be going well, though they were complicated by the fact that she was away for most of the summer. I made my views on polyamory clear from the beginning, and she didn't like them at first, but seemed to be warming up to the idea.
As of this week my first lover took up a religion out of nowhere and want to excise sex from our relationship (hardly mindful of the massive collateral damage that will cause, even without the other problems with religion). (I will probably want to write about this separately, but I need to pull myself together first.) And my second lover has pronounced having second thoughts about the idea of polyamory and will not touch me. The timing is coincidental (I'm pretty sure), but it hurts just the same.
After years of reflection, I think that I'm about as natively poly as it's possible to be. I have focused my efforts on serious long-term relationships, since those seem by far the most valuable to me, but I wonder if this is causing me to miss my connection with other people who are more sympathetic to polyamory. I have not found a lot of sympathy for my viewpoint over the years, not that people have ever been keen to offer actual arguments to support the monogamous status quo. The most substantive points I've ever heard raised are STIs (which are a distraction, they apply equally to serial monogamy and there are well-known steps that can be taken to avert the risk) and jealousy. I don't seem to be capable of feeling much jealousy, and have at times tried incredibly hard to get my lovers to pursue other interests so they would appreciate polyamory better. As far as I can tell, people who do experience a lot of jealousy have just as much to gain from being more open and honest about their reasons for exclusivity (instead of treating it as a conerstone of morality itself), but I know how arrogant it would be to pretend I understand their perspective. Ironically, jealousy doesn't seem to be the problem in my current situation. Despite knowing that it makes things more difficult, I have gradually developed the resolve to insist on polyamory, refusing to enter an exclusive relationship on principle. I have hoped to achieve major long-term gains this way.
So in the last few days I have been depressed and irrationally thinking things like "girls will never be able to handle polyamory" (not that I've encountered many other guys who like the idea, and there's plenty of directly contradictory evidence on the internet) and "I have to do it the way other people want if I'm to get any love at all" (yet best-selling books have been written by people who do it the way I'm trying to go for, trying to encourage others to do the same). Then I saw this post, the first time I recall polyamory coming up on LessWrong in a major way (I've been lurking since the beginning). LessWrong somehow feels a lot closer to me than other random places on the internet. It breaks my heart, somehow in a good way, to see a group of people notice the insanity of mononormativity and start a discussion about how to "hack themselves poly", a noble and courageous task I couldn't even begin to understand since I started out this way (and I don't really know what it's like to stare down the barrel of one's own jealousy).
So...carry on.
What??! Oh my, how differently this works for me. I am attracted to many, many people, and they are ALL irreplaceable, nevermind relationships, my very attraction to them is irreplaceable! People are fascinating and unique, and in every case there is a mixture of common, less common, and unique features that contribute to the attraction, as well as memories of experiences I shared with them. The idea that by pursuing an attraction to someone else in anyway means that any given attraction is not special is an insult to my feelings! In many cases, I love these people more than I can even express and would, were it not for limitations of time and persuasion, do more things than there are names for with them, and indeed whole different sets of such things with each one, and that's if I couldn't persuade anyone to do them in larger groups. I am unspeakably sad that I almost never get to do any of things, and unspeakably grateful that get to do even the more mundane things I ordinarily do with my friends, and indeed to have met them and interacted with them at all.
I am not a very successful poly in real life, mostly I think because I have literally never met another poly and have therefore been operating on the basis of trying to convert monos, but when I occasionally have periods of success I am so elated that I barely know what to do with myself--alas, I fear in many cases I am not even able to communicate this to my partners. So please, please, if I love you, no matter whatever else I do, think anything but that you are not special to me!