I know that a lot of it comes from deep fears and insecurities of inadequacy and ultimately of being left.
So are you looking to learn to live with it and reduce it to a lower volume? Or eliminate it? What are you willing to do? See a counselor? Something else?
If you are approaching polyamory mainly because you believe this
We both agree that monogamy is usually unhealthy and often destined for failure for all the reasons that you are all very aware of
that reasoning seems more like "NOT monogamy" rather than "FOR poly" to me.
What are your other reasons for not wanting monoshipping?(Everyone is different.) Could they also
apply to polyshipping? Is reconciling that something you could need to do so you can achieve your goal of becoming more secure in a polyship?
For example, if you believe monogamy never works because people eventually cheat, you have to reconcile that fact that sometimes people in polyships cheat also. It isn't the shape of the relationship but the person doing the cheating breaking agreements.
I'm not saying cheating is RIGHT in either case. I'm saying it's going to feel hard to feel secure in a polyship if you haven't made peace with things like that being possible in BOTH monoships and polyships.
Are you feeling like both of you are entering the polyship with "one foot out the door" already?
How are you in the habit of talking to yourself? Do you talk down about you to you in your head? That could be another thing to work on to break so you can feel more secure in yourself.
Could this help any?