Growing up in my family, before I understood BPD and family dynamics, I thought BPD mother was the one with the problem, and that somehow, my father was a victim of her behavior.
This wasn't the case. When one family member has a disorder, other family members take on behaviors in response to that, and that can keep the family in a sort of balance, even if the behaviors are dysfunctional. Learning about the Karpman triangle dynamics helped understand one of these patterns.
https://www.bpdfamily.com/content/karpman-drama-triangleFamily patterns can be arranged in different forms of the triangle. In my family, my father was mostly in rescuer/enabler role. BPD mother was in victim perspective- perceiving herself a the victim in the scenarios. I think this is the perspective that a person with BPD has.
The triangle can be configured with different family members and while the pwBPD sees themselves as victim, other members can be either rescuers or persecutors, and also to each other with different members in one of all three roles. A main point is that all three roles are dysfunctional.
fBPD mother was upset by anyone or anything- Dad took on the role of rescuer, to her side, against anyone who she felt upset her- even if it wasn't the fault of the person she was upset with. Dad was not a passive victim of BPD mother's behavior, he was a part of the dynamic between the two of them.
So yes, it is upsetting to have a trusted family member turn on you like that. Although it's upsetting, it may give you clarity to step back and see this as a dynamic in your family. Sometimes these dynamics are automatic and even learned through growing up with dysfunction and can feel "normal" behavior to the person.
Here is the actual secret to being in rescuer mode. The person in rescuer mode is actually rescuing themselves from their own emotional anxiety when they do that. Anxiety over the pwBPD's emotional distress, and wanting to over fix things. It's not actually helping.
Would you and your H be open to marital counseling? Because the two of you need to be on the same page over your BPD-D and even though she's the one with the disorder, it is affecting your relationship.
Where your H crossed the line was that he was feeling anxious over the kids having dinner alone. Dad felt in victim perspective (these dynamics aren't just with pwBPD- others do this too). He blamed you, then he crossed the kids' boundaries- presumably in rescuer position to them- but also to himself. The kids reacted appropriately to their boundary being crossed.
Rather than to jump into "H was wrong" I would say "H is following a behavior pattern that is "right" to him. We do what we know how to do- so take away the right wrong thinking and look at the bigger picture- all family members have adopted disordered behavior patterns.
While the focus is on your BPD-D- turn it to you and your H- counseling will help you gain insight into your roles in this dynamic so hopefully you can learn more functional ones- together. You and your H need to get on the same page when it comes to the kids- and this is a path to take to get to that.