I guess this is why everyone says not to try to teach your BPD partner.
I kind of thought setting boundaries was a sort of living DBT, to teach him by experience that it's not worth it to rage/act abusively.
But I guess if I am learning from this thread, it would be that setting boundaries is a life-long project, something that will always have to be done to enable us to live side-by-side with our BPD partners.
Well, first of all, boundaries are for yourself. Invisible lines that you set for yourself, how to behave and deal towards people and many situations in life. There are core or permanent boundaries (like - I won't steal no matter what, even if there would be no penalties) and those that can be altered and are flexible. You need to see the lines that are in-sync with you, regarding your relationship with pwBPD and their behaviour.
Based on my experience with high-functioning BPD wife, you
can teach them it's not worth to rage/act abusively. But they need to feel the consequences and get to the point by themselves, even if you or therapist guided them "secretly" to get there.
Depending on severity of the BPD issue and
your own capacity, this can be either a long and tiring process or not.
But relying on their empathy that they will see the damage they've done and learn from the mistakes is not good. They can feel so bad internally that any damage they make will seem justified and if you act or respond, they will have someone to blame too. Every bad respond to their anger/rage will just prolong the "education" period for them to learn and try to move on.
Every time pwBPD has even the slightest chance to put blame on something or someone else, they will do it, make no mistake. And you will find it hard to resist, because at times they will be very rude, you'd want to scream out loud - but don't engage.
So yeah, lessons from DBT are very good for them, but unless pwBPD goes to a professional, you have to be really careful when you apply them yourself. See yourself more as a mentor/coach,
you be the example, rather than as a teacher that scolds, punishes or expects the lessons to be learned.