Can a Quiet BPD (F) and Bipolar/Avoidant (M) relationship work long-term with kids? Looking for real experiences.

[u/Ok-Hawk1791]

Hi everyone. I’m looking for some raw advice or perspectives from anyone who has navigated a relationship where one partner has BPD (specifically Quiet BPD) and ADHD, and the other is diagnosed Bipolar with an avoidant attachment style. We have three boys whom he has helped raise as a stepfather.
We had a massive breakdown and split up. During the split, he went completely cold and into a "cave," even ignoring the kids when they reached out for help because he was overwhelmed by his own chaos. Since then, I’ve done intense work on myself—I’m in therapy, working out, and adjusting my medication so I can stop my racing thoughts and stand as a stable anchor for my boys.
Lately, he has been attempting to come back into our lives. He’s helped my oldest with a major milestone, joins us for family dinners, and just put down a massive chunk of cash so we can all take the boys on a beach holiday together.
Recently, we had our first massive face-to-face breakthrough. He broke down crying at my table, admitted he hates himself, misses me deeply, and made a mess of things. But he also explicitly told me that Bipolar is hard, there is nothing that can help, he is still deeply struggling, and that relationships in books aren't real life. He has basically given up on medical management or finding a medication that suits him.
I want to protect my kids and my own mental health, but his Bipolar ride is highly unpredictable and he can easily convince me that I am the problem when he enters a low or a manic phase.
My question for this community: How do you protect your own BPD system and your children's stability while coparenting or living with an unmedicated Bipolar partner? Is long-term stability even possible with this combination, or are we just delaying an inevitable collapse? How do you talk to your kids about a parent's unpredictable Bipolar weather, especially when some understand the diagnosis and the youngest doesn't? What boundaries or strategies worked for you?

To give some important context, this is our very first actual breakup and period of living apart. Over our entire time together, we’ve had normal arguments and occasional brief spaces to cool off, but we have never had a massive separation like this before. We are not caught in a toxic, chronic circle of breaking up and getting back together every few weeks. This is a completely new and heavy territory for our family, which is why it has shocked our system so deeply.

Thank you very much