I’m in a closed MFF triad. My partners raise 2 children together; I have none. Together we have been looking into getting our own place currently we stay with family. Our partner decided well realized she doesn’t want to be in a closed triad, feels trapped and wants to be able to date other men which we both know our boyfriend wouldn’t support. She’s suggested it and he’s turned it down. She’s also decided she doesn’t want to tell him until after we move. He knows none of it she told her best friend and I. Not sure what to do? I don’t want to betray her by telling him but can’t make her. So I have no clue what to do being “in the middle.”
You’re not “in the middle,” because this is immediately affecting you and whether you will have a stable living situation in the future. Moving is incredibly stressful, and having to end leases, find roommates, split belongings, etc. is messy and difficult. You have a right to act to protect yourself from future problems with your housing.
You can let her know that you think this needs to be discussed before the move, for the sake of everyone involved. Tell her that you’re worried about what will happen if this comes up after everyone moves in together and you don’t feel okay making that move knowing that this shoe is set to drop. You can let her know that you’ll need to tell your partner why you’re backing out of the move until this is resolved, and she can choose whether to tell him first herself, or let the chips fall where they may.
This is not about you betraying her; this is about you protecting your future self from horrible housing drama, which is, in my opinion, one of the worst kinds of drama. If this wasn’t directly affecting you, my advice would be different; but since she plans to keep this to herself until after everyone moves in together, you are well within your rights to put the brakes on that move until this gets worked out.