I agree with everything london said. You are lucky to start polyamory like you are doing!
I started fresh, like you are doing, and only ever have had open / poly relationships. To me this has worked fine; the problems in my relationships have never been caused by polyamory, but rather something totally else.
One piece of advice that I have to give is the most common poly advice: communication, communication, communication. Do not count on single words like "polyamory" or "open relationship" but describe what these things mean to you, and by all means try to find out if the other person has undestood you correctly.
One example about this from my life: I always told my potential partners that my relationships will be open and I like the idea of polyamory. Discussed this several times with my now husband CJ early in our relationship. Still, he thought that the "open relationship" was over since we started being "serious". More communication and problem solved. Next time the same thing after we got married - I did not realize this should have been discussed again before the wedding. Well, we did discuss it after the wedding, and it ended up fine.
And then the "polyamory" part. We discussed it many times, and still... After I fell in love with my OSO Mark, I realized that CJ had thought that "polyamory" is the same as "unicorn hunting". Since we both had agreed that unicorn hunting is a bad idea, CJ had assumed it was the end of my desire for polyamory... and we have gotten over that, too.
All three of those incidents could possibly have been disastrous, but they weren't. Honest communication and responsibility of our own emotions has been the base of our relationship, and with them we have conquered these severe misunderstandings.
I am a woman with two male partners: CJ (legal husband) and Mark (no label added).