I've actually been poly for most of my adult life. I only ever had two monogamous relationships growing up, one of them an LDR that evaporated when it became clear we weren't going to be able to relocate to be with each other. At this stage in my life I had already heard of polyamory and had grown up vaguely wondering why nobody ever seemed to do it, and suspicious of the general refrain from adults I asked that it was impossible or unethical.

It seems to be an instinctive matter of orientation for me -- I love deeply and intensely, but I don't seem to stop forming such connections once I'm in a relationship, and once I started dating other poly people, I never really went back. I find it difficult to conceive of being in a monogamous relationship now; I'm sure there are at least somewhat realistic scenarios where pragmatic factors could cause me to not pursue other relationships, if I were living in such a situation with a single primary partner who wanted monogamy -- but that's not where I find myself today, and I have absolutely no desire to trade my current life for it. I'm also quite sure I wouldn't be as happy, in such a situation, as I am in my current relationship network, and would regret the sense of lost opportunity.