Hello and welcome! OK, yes, it is a bit confusing, so I will try and reconstruct what you wrote...
You have been with your girlfriend for nine years, and she is monogamous. You two live together.
You have another girlfriend, with whom you started having an affair while she was also in a monogamous relationship with someone. So the two of you were cheating on your partners for a few years. And your second girlfriend is close friends with your primary girlfriend.
Since then, your second girlfriend ended her other relationship and has been staying with you and your primary girlfriend. You want your primary to consent to a polyamorous arrangement with you and your second girlfriend, but she's mono and doesn't want to.
Does your primary know you cheated on her with her friend?
Now, your second girlfriend met someone else who is poly, and he has the consent of his wife to date her. She's known him for ten months (a good amount of time to get to know someone) and wants to start a relationship with him, but you object. Why?
You have been supporting her financially? Does she have any of her own income? Was there ever an agreement for her to be faithful only to you? I don't see why she can't date whomever she wants. Just because you give her a place to stay doesn't mean you own her. What exactly is your problem with her dating someone else, since you also have someone else? Or have I misunderstood?