"The problem is me. I worry about the arguments and/or endings that I experienced with my ex. I want to include another partner in all aspects of my life and not having restrictions/rules. Too soon to include someone else? Cold feet?"
Have you just laid this out to him, straightforwardly? It may be too soon to include another partner in your life in the way you seem to be describing, but it's not too soon to be talking about it. I mean, could you just show him your thread here?
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.