I'll offer that any relationship that is on-and-off frequently--which is how I understand your relationship with your ex was--is unstable. The on-and-off serves as a warning that you should walk away at the very next "off" and never look back. Stable relationships, in my experience, aren't anywhere near that volatile.
Yeah, it sucks that some relationships will never work due to one person having a poly bent and the other having a strong mono preference. That's just one of the many things in life that won't work in the fashion we'd like them to work. I've a list of ladies I've accumulated over the years that I would have loved to have gotten seriously involved with and didn't because I could tell there were some basic incompatibilities; they've made for wonderful friends, though.
You now have the chance to sort out exactly who you are and what you want and build the sort of life you want. Once you get involved in doing that, you'll be able to find new people who will fit in your life, as long as you're the sort of person with whom others can fit in with.
That last might be the key. From what you described, you're currently not the sort of person others can fit in with easily. You describe a lack of relationship skills--blowing off what your partner tries to communicate and so forth--and that sort of thing may be the cause of all your relationships falling apart at once. Sorting through that is going to take time--of which you now have an abundance--and a critical eye aimed at your behavior.
Welcome to the boards.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.