Hey 1stTime, welcome to the boards and thank you for your kind words! It's really nice to hear that reading my story has been a positive thing for you.
As for your question, it began for me in high school. I'd dated people monogamously before. One summer I had a big crush on a female friend of mine and was planning to ask her out, but instead she started dating a guy friend of mine. This particular guy had long had a crush on me. I was so jealous of both of them, and so attracted to both of them! It just drove me crazy. There was some fooling around and a lot of flirting, but things didn't work out between the three of us. During this time I did a lot of reading online about polyamory.
Later that year, I ended up dating two guys at the same time... that didn't go well, they tried to be cool with it but ultimately weren't and I ended up breaking up with both of them. Then, shortly after high school ended, I got into a serious relationship with an older guy, we'll call him Ziggy, who had a five-year, live-in relationship with another woman who knew about him and me. So, in fairly rapid succession I went through a variety of different poly situations... pining after a couple, being the hinge of a V and then being a wing of a different V.
After things fell apart with Ziggy, I started dating Davis. He and I were monogamous together for three years, aside from one incident where I cheated on him with Ziggy (I've talked about this a little in earlier posts). I was monogamous with Davis initially because he wanted it and I wanted him and it seemed like an easy thing to give him. At least it seemed that way until it wasn't and I cheated and we eventually split up over it. *sigh*
Poly feels very, very natural to me. Why should what I do with one person have any impact on another person as long as I'm being honest and safe and considerate? Like, if Gia and Eric and I spend an hour playing video games, how does that affect Davis any more or less than if Gia and Eric and I spend an hour having hot, safe sex (*siiiiigh*)? I have fairly compelling proof that loving one person doesn't stop me from loving another person -- if it did, Davis and I wouldn't have broken up in the first place.
In my heart, ever since that first couple I fell for in high school... hell, maybe since before that, when I first realized I was bi... I've always thought that being with a guy/girl couple would just be amazing. And reading about poly stuff, seeing poly situations depicted in a positive way, just makes me so *happy*, the way seeing depictions of women loving each other made me feel happy and validated when I was young and still does now.
So, I didn't exactly "decide" to start living a poly lifestyle again post-Davis, but it was something that was natural to me. When Gia suggested that we date I didn't see any reason not to and, in fact, saw the situation as something close to my m/f/f triad ideal even though it's not exactly that.