You sound like you have summed it up well. You've even tried it on for 9 mos already and still feel the same -- polyshipping is not for you because are not "polyamorous" or "monoamorous and poly-friendly."
You sound like you are monoamorous (love only one) and polysexual (willing to have several lovers.) So this configuration is not one in which you thrive.
I have been trying to decide if I should somehow keep trying to make this work or if I should go my own way. Neither option is what I want.
There's two kinds of freedom. The freedom TO and the freedom FROM.
There is no " I want the freedom TO do X" here because you do not want to do either option. So the decision then is about "I want freedrom FROM."
When you look at it that way? If what you want is freedom from
being in polyship -- which option is the path?
- Staying in the polyship with him and her.
- Leaving the polyship.
Maybe that change in perspective could help with your emotional management?
Hang in there.