Welcome! I hope you find comfort here. There are a lot of really emotionally mature individuals here- so I hope you are able to find what you are looking for.
I read all of your posts and this is what I am hearing.
You have realized and explained to us in detail of how severely dysfunctional both of your partners are and also how unhealthy and dysfunctional your relationships are with one another.
I don't think there is anyone on this forum who would disagree with that.
And- you have chosen a few classic justifications which will allow you to remain in them.
She loves me. She knows me so well. Etc. etc.
And- the most fascinating justifationof all is.....
Oh- well, I'm pretty F'd up too anyway.
I would suggest that you decide what level of emotional maturity you would like to experience in your life. I don't want to make any assumptions, but I might wonder if you came here in order to be confronted.
Your ability to justify living such a dysfunctional life is quite developed and may be fairly indestructable at this point.
If you do desire a more emotionally functional life, i would suugest that you find a psychiatrist or psychologist that you can work with.
I don't really see this as a poly issue, but you may get some good feedback here anyway!
Good luck and I hope you keep sharing!
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.