This is an extension of some thoughts going on in another thread
The question, paraphrased is: How can one risk a current relationship with someone you truly deeply and really care about (Person A) for some new person you just met, hardly know and have next to no bond developed with (Person B)?
My answer is that quite simply, that my experiences with Person A have led me to believe it is worthwhile to pursue and entertain people I am attracted to. In at least the case with Person A, it has led to a satisfying series of interactions which I wouldn't change.
This is sort of the mentality that brought me to poly. I certainly DON'T want to throw away relationships with strong bonds that I've developed over years for some NRE with someone who is practically a stranger. But I DO want to find out if that stranger might be another "Person A". It's a reflection of my platonic life as well. I have a few good friends, some of whom are my siblings, some are past lovers, but they are all unique and in all of these relationships there was a time when we were unknown to each other.
The problem recently I've experienced is that I was with Nyx who agreed to try poly with me, but then anytime I started actually dating or interacting with someone romantically besides her we would have a meltdown, tears and hours of conversation to try and get to a stable place again. The stable place usually involving me also dropping any present or future plans I had of dating for a little while. A little while passing, another attempt to actually shift "mono" to "poly" and another break down or even break-up, the circle continued.
Thing is, Nyx is very important to me, but she doesn't see things the same way I do. We are not together now, but we hang out and I know we would like to find a way that works for us.