I've been her before, trying to claim polyamory while distancing myself from existing relationships. It wasn't malicious and I didn't even realize I was doing it, but it was bad and I learned a lot of things about myself in the process that I had to work hard to change.
And that's the point I wanted to make. SHE is the only one who can change her behaviour. It's not your job, responsibility, or right to change her and honestly even if that was what you were trying to do here, it's not possible anyway. She won't change until she feels like she needs to no matter what you do and in the meantime you are being put through something that is, at the absolute bare minimum, borderline abusive.
A new relationship is not going to help fix the problems (real or imagined) that she has with your current relationship. It's only going to make them worse. There's nothing wrong with polyamory but it has a bad rep because so many people think that they might be able to fix things by bringing a third person in. I'm not excusing what she's doing to you, she is absolutely wrong and it needs to stop asap, but she might not realize yet just how wrong she is. You've talked to her about your concerns, you've tried to change things she's complained about, you've tried to be understanding and accommodating... There's not a whole lot else you can personally do about it.
My advice depends on whether or not you think the relationship is worth saving. If it is, get marriage counselling. Nothing you say (short of an ultimatum which is a bad way to go anyway, it'll just start a fight) is going to make her seriously listen to you but maybe if you can talk to her with a mediator with a degree and nothing to gain in the room she might actually sit up and pay attention. If it's not, it might be time to write the relationship off. Reading through the thread gives me the impression you're going to be looking up counselors, but you are the only one who knows yourself, your partner, and your relationship well enough to make that decision.
