I am in a "vee" Nim, but I also have a girlfriend, Derby, and two other love relationships that are designed in such a way to suit me and those I am in them with. My "vee" with Mono is my direct family though.
As for how long? Poly all my life, out as such for 15 years and fully practicing what's right for me in the last 3 years. I had no idea it would turn out this way, but I did ask for all my needs to be met in harming none and helping all and I have been gifted that ten fold. I am very grateful! I have put the work in and it has paid off. I continue to do that. Part of that for is writing on here for me and helping to create a loving yet honest and open space for poly people to be supported and form community beyond this forum.
I met my husband through a marriage to a woman who is a love of my life still but monogamous and uninterested in actively being a love back.
I'm happy you have come to some understanding of yourself! Very exciting for you