Well, it seems to me that she is not really asking him to break it off with you. She just doesn't want to share her home with you anymore. You've only been living together five months; perhaps the first three months you and her husband were together were much easier for her to deal with because it wasn't in her face all the time. Maybe she just likes to maintain a household differently than you do and finds you difficult to live with. Or perhaps she's an introvert who feels her privacy has been invaded and she needs more space and time to herself.
Whatever her reason, I don't think she's being unreasonable to reject cohabiting with her metamour. I never really understand the importance people place on every partner all living together. It's hard enough to live with one other person! She hasn't told him to end things with you, so that at least shows she is willing to accept his polyness. She simply prefers to be the mono in a mono/poly arrangement. Nothing wrong with that. I see no reason to villify her for it.
However, if she does want a separate place to live but can't afford it on her own and wants him to support her, looks like she will have to work more to contribute to that. It would seem that this needs to be discussed. You should all sit down and look at the logistics of such an arrangement, and see what the possibilities could be, so that everyone is happy or at least not overly compromised in trying to achieve that happiness.