This reads like a journal thread. Could ask a mod here
to move it to the journal area
if you intend it that way.
Am I reading this right? You started up having a cheating affair with him, and are now worried he's kinda cheating on you/breaking agreements with this woman? There's a lot of details in there but is that the bottom line?
At the very least you have communication and respect needs that are not being met here. You have been lied to, and this has broken trust. Is he talking hot air or actually making changes to his behavior to make ammends and rebuild trust?
It is on you to discern if he's used up his 3 strikes you are out, if the effort being put in is the right amount or too little too late, and if you are still willing to receive this sort of treatment if things are not changing at or or not enough. You have been the victim of abuse in the past -- be VERY careful with your mental health, emotional health, physical health, and spiritual health. Do not mistake what you wish it was for what actually IS.
If he NOT change his behavior, how will you behave in self respecting ways in your own conduct then? What natural consequences have you told him will happen?
I really do not want to give up on what could be a beautiful poly/open relationship but I also don't want to find out I am being played in the background.
How are his behaviors demonstrating beautiful loving open/poly kindness toward you?
I am sorry you are hurting. I hope getting to write it out and vent at least helped some.