I feel like your meta has some really valid reasons to be struggling with unexpected change and not feeling sufficiently informed about things happening in her life. It's not your fault, in that it's communication problems and possibly different relationship goals between her and your mutual partner. And yet, she probably does feel pressured to accept you, which makes it hard to be friends.
Putting your future living situation on the table for everyone to discuss their goals and needs and hopes, and ultimately the practical level of getting there, might take some pressure off. Her partner being poly and with you is maybe not negotiable, but whether you'd each prefer to share a household, have adjoining/nearby residences for each couple, or live in the same city but not close to each other, probably is a good topic for discussion. Maybe you would be happy to live in the same house so long as it had two master suites, or maybe it would need two kitchens. I know your dream house(s) might not exist, or might not be as financially practical as you'd like, but this is something you can talk about on both short and long term levels.
If she jumps straight to wanting to live separately, then I'd say you should consider immediate practicalities of moving out. Can you afford it? What if you had a roommate? (Would you want roommates?) Could you and he afford it? How does everyone feel about a place that's a you-and-him financial project? (You included - could be too big a step for you at this point in your relationship.) If you chose a good place for you and your budget, how far apart would you be from the existing place? What's that going to do to time and date nights and etc?
Note that the point is to find something that meets the needs of everyone and gives people a fair share of their wants, and not to be adversarial. (But also note that you might be taken that way, if your meta really feels like you should defer to her all the time.)