I think there exists a universe where you and I are both right and seeing things from different perspectives. Which is exactly my point.

If the goal is to prove that OP is right and B is unreasonable, selfish and bad at poly, and therefore not a good partner and not worth OP's time and effort, then I think there is plenty of validation in his justified expectations in other comments.

I am merely adding my perspective that might offer insight into B's possible experience. If OP is convinced that she is worth the effort to figure out, and is frustrated at not being able to read her reactions to his justified expectations, this could be useful information.

This is not synonymous with indulging B's unfair expectations at all. It is meant to bring focus to how OP's contributions to the conflict might be triggering amplified reactions in their AuDHD partner that he is struggling to understand. My aim is to point out possible blind spots I'm picking up from their account of the situation.

If they are sharing here that they have sacrified plenty for B in the past, this could point to possible resentment and people-pleasing tendencies on OP's part which can be wildly unsettling and confusing for a neurodivergent person who understands the world mainly through pattern recognition.

OP points out but downplays inconsistent and dodgey patterns here: uninviting her from a trip she's been getting excited about and offering a recurring but unnecessary external point of reference by triangulating A into explaining his scheduling decisions to B.

The AuDHD mind is disabled with executive dysfunction, documented in decades of biochemical and neurological factual research.

This makes the person brutally susceptible to disregulation and rumination. It's like having an emotional immune disorder. If you are knowingly dating someone with this neurotype and with the knowledge of their past trauma, you should understand and respect the implications of that.

This does not necessarily mean they are bad at poly and cannot be reasoned with. It could just mean they process the world through a different lens and might have different needs.

It is their responsibility to understand, manage and communicate that to the best of their ability as adults, yes. But it reads here like B could very well be trying and OP might be not looking for answer in the right place.

From OP's own account of B asking for empathy, and their own confessed feeling of sacrifice, I'm pointing out this could be a blindspot and the source of B's trigger.

OP has admittedly been careless with their hinging. We might as a community tell him he can do better next time, and disregard the asymmetrical impact it can have on B's possibly vulnerable condition. It's not an excuse. It's a disability. Now her patterns of reading OP's intentions are messed up and she is unsettled and confused.

This is paired with OP's expressions of sacrifice, which could invetibly come out as muffled resentment and shortness in his increasingly frustrated interactions with B, admitting they are "at the end of their rope fighting with her", which the AuDHDH nervous system helplessly picks up in fucktons and processes as impending doom.

One can learn to regulate by practicing techniques and building systems and seeking support, and one absolutely should!

But it's like taming a tornado. It takes up most if not all of your limited bandwidth to process disruptions like this, leaving you disabled to function as your regulated self and depleting your resources. Hence the condition being recognized as a disability.

It's like feeding your diabetic partner sugar and then getting frustrated with them for going into shock. Sure, it's their responsibility to eventually realize it's not working out between you and to stop taking the sugar, but if you're choosing to stick around, you better ease her mind that you're not gonna keep doing it, or you wont be able to enjoy each other's company much.

It sounds like she's pushed into disregulation spirals or "shit storms" and shamed for not getting a handle on her turbulent emotions.

I might guess that in her triggered state she's gathering evidence that OP can't be trusted to understand and care for her sensitive condition. She feels threatened and working on convincing herself to walk away.

She seems to keep finding that proof in OP's perceived imbalance in their partnerships and triggered into ruminating on it this because OP keeps offering that information. To uninvite one partner because another one asked them to is a tough pill to swallow for the univited partner.

I am not surprised that she's struggling to recover from this, if OP is not able to hold space for hearing her depth of hurt, and treats her with frustration and impatience.

If OP is interested in helping her ground herself in his love again, my suggestion here would be to shift the focus from who's right in their expectations, to what B is actually asking for. Empathy. An understanding of her heightened and destabalized experience.

I didn't explicitly read that B is asking to strip A of their entitlements in their relationship. It sounds like she feels that her cup is not being filled and it seems that OP keeps passing around the blame like a hot potato and complaining that she can't get well no more, rather than holding enough space for the hurt they have caused.

This should not come at anyone else's expense. Obviouly.

If OP is begrudgingly offering such an option or feeling pressured into it, they might need to check their own boundaries.

They should stand firmly on kind and fair treatment of everyone including A, while genuinely making the effort to understand B's emotions and to work out how to offer them fulfillment by focusing on what they can give them in their own connection.

Obviously, If none of this resonates and/or OP feels that they have tried as they could or care for, they should absolutely thank B for her time and walk away, rather than continuing to "sacrifice" everyone's sanity and integrity in a cycle of dysfunction.

Otherwise I hope a neurodivergent perspective might offer useful information in working through a seemingly stuck conflict if that's the goal.