As we just joined last month, I had to go back and re-read your posts from the summer. I'm sorry for your breakup - long term relationships are never easy to get over. From what I gathered, it seemed like you discovered being poly in the middle of your relationship, and had to go through the whole gamut of turmoil while trying to be true to yourself. That's particularly rough as the expectations and world-views of all people involved are turned upside-down. When my wife and I finally talked about our interest in poly and got it all out in the open, it was only after we hit rock bottom. I'll spare you the details, but suffice it to say it was the hardest conversation we ever had. If we hadn't both
been for it, I know it would have only gotten worse and probably would have ended in divorce. I'm going to guess that going through NRE with the new person was both exhilarating and terrifying, because you felt like you couldn't have one partner without the horrible loss of another. Happened to us too - and ours was off-limits to boot!
First off, damage control - is anything salvageable? It sounds like you had really deep connections to both partners. I personally tend to slash-and-burn all of my relationships (including friends and jobs) when I need a fresh start. I've learned over the years to instead let them fizzle out gently, and as a result have rekindled things later when both parties were in a different head space. If you feel that you need a brand-new clean slate, then so be it, and more power to you. Otherwise, talking to them openly and frankly would at least let them know where you are coming from, and they may surprise you. Considering that you've already taken action, I think either option is reasonable for you (among others - only you know what's right for you in your heart).
I think that for better or worse, you sound like you're in a healthy place right now, and that's good! You're healing, and soon you can move on but with a new advantage you did not have before: Now you know more about who you are
, and can actively engage poly-open people in the future. You have the unique perspective of time and experience, and this "first" can't happen again.
Although we have different backstories, it sounds like you're starting to look for new poly friends and relationships too. Start with the friends part, and glean every last nugget of truth you can from this site while you're looking. There are a ton of awesome people that are an endless resource of good advice, insight, and help. Oh, and sooner or later, someone will tell you to use the search function, so I'll just get that out of the way right now.
Good luck, and welcome back!