I am polyamorous, but it is interesting to ask why that is true. What exactly is it that makes me this way, and why did I make the choices I made? Part of it is simply being born this way - like most people I have the capacity to love more than one person at once. However, there is a huge gap between having that capacity and deciding that doing so is the best way to live one's life. Getting from 'possible' to 'do it!' took a lot of thinking and experience which is particular to me and my life. Other people have different biological baselines, experiences, and priorities so they will end up at different conclusions.
The primary things that affected my choice are sex, poly theory, and a singular experience of new openness.
Sex is a big deal for me. I have a big sex drive and very much appreciate variety of all sorts. I want sex when I am sad, happy, stressed, calm, tired, energetic, and all places in between. My primary love language is touch and for me the biggest and most impactful component of that is sex. If I am not getting it I don't feel loved in the romantic sense. For many years I felt that while sex in my marriage was good I could get extra happiness and satisfaction if I had more partners and more options. If I could just find someone else who wanted to have sex constantly and then visit them for 30 minutes every day that would be super duper right? (Good *%&#$ing luck with that, btw.)
More intellectually compelling but less viscerally powerful was my liking of poly theory. I have always found jealousy distasteful and I dislike the idea of blanket social contracts with no room for individual preference. It is completely cool if people want to be exclusive but it bothered me that doing so was considered the only moral choice. I like the idea of every set of partners negotiating the things they need and granting their partners the freedom to do whatever makes them happy as long as everyone is getting what they need out of the relationship. Being able to arrange the relationship to suit the people in it rather than arranging it to placate those outside of it makes so much sense!
I also grew to love the idea that love is not exclusive. I can snuggle on the couch with two people I am romantically entangled with simultaneously and the love I feel for both of them does not diminish because there are two of them. (Double snuggle makes me smile so hard it threatens to crack my face.) It is both possible and common to be happy to see a lover be happy and deeply in love with someone else; such feelings are called compersion and it is a big selling point of polyamory. I so much approve of the idea that love need not be the source of anger, need not require tight control. Even if I weren't suited to polyamory or couldn't participate due to circumstances I would approve of the theory very much.
So sex and poly theory both pushed me to want to be polyamorous but what truly cemented the deal was an experience I had in the very early going. After deciding to have an open relationship I felt a huge change in myself. I felt walls that I unconsciously erected around myself fall away and a new sense of immense freedom took hold. I took my vows of monogamy incredibly seriously and made certain to never put myself in a position where being unfaithful was even feasible. Letting go of that control, allowing myself to flirt, to express interest, and to let my emotions flow where they wanted to instead of clamping down on them was *amazing*. I had exerted such force in keeping myself on the straight and narrow without even being aware of it that being able to skip doing that completely was a transformative experience.
It got even more powerful when I actually did something about it. The first time I confessed that I had a big crush on someone she was a friend who I knew pretty well - we had plenty of experiences together and a degree of trust. Her response to my confession blew me away though "But I didn't even think you *liked* me..." That hit me hard because I suddenly realized that those walls I had set up around myself weren't just keeping me in check; they were actively keeping people away. I realized that I had spent years pushing away people I liked, respected, and wanted to know by keeping myself unavailable and distant. It made me wonder how many people had found me cold and unfeeling and how many friendships I had torpedoed by unconsciously trying to keep to my vows.
That experience made it clear to me that I cannot go back. I can't again be someone who walls himself off from people, who when faced with someone wonderful immediately takes a step back instead of forward. I fall in love easily and do so with people and in circumstances that aren't necessarily a good idea. The only way to prevent that is to keep myself so far back emotionally that it damages any chance of a good friendship. Doing so is far too great a cost and that isn't a promise I will make again. That doesn't mean that every time I fall in love something has to happen - after all, sometimes love just ain't enough - but it does mean that I must live in such a way that love may happen and that it is okay when it does.
I showed up to the poly party on the back of lust and intellectual appreciation of a theory. I am staying at the party because being here makes me happy and because it makes me a better person. I can't think of a better set of reasons to do anything.