I think I'm improving in boundary setting in that I am no longer always 'taking the bait'. When I don't 'play', he has no fuel. As a result, his tantrums are less intense, and shorter in duration, and the frequency is reduced. I see this as a move in the right direction.
That sounds likes it going in the right direction

What method are you applying to enforce your boundaries?
My loneliness stems from his distancing himself from me. You see, as I set boundaries, not only does the negative stuff get reduced, but also the good stuff. It's almost like he's paying me back for setting boundaries.
He is. Some pwBPD do silent treatments/extinction bursts. Has he said anything about it, or did he just start clamming up?
My mother died a few months ago. He barely could make me a cup of tea on the day of her death, and used his 'bereavement' time at work to travel across country home to her funeral, only to tell me 'I'm going to such and so town to visit my friends.' As a result, my family no longer has respect for him. Then, when he could not be supportive a few months ago when mom died, just this past month his 34 y/o daughter had to put her dog down. Boy was he on a plane in no time to 'comfort' his daughter during her 'grief.'
I am so sorry to hear about your mother. I am also very sorry you had to endure that loss alone. I know it must have hurt to see him support someone else but no you when you needed him the most. It's very possible it was 'punishment' since he might have you painted black right now. Sometimes... .they just don't make too much sense. My H can cry about a neighbor we don't even know leaving in an ambulance... .but couldn't have a kind word for me or hold my hand when my grandmother died.
I have few friends, b/c of his behaviors, but the ones I do have are solid rocks. And I find my anxiety is reduced when I spend time walking the dog or playing with the cat. I have other hobbies; I quilt, and I make little blankets for the NICU babies at the Children's HOspital. I like to garden. These are ways I take care of me.
Very good! It's good for all of use to take time for ourselves and find our own joy... .I'm still working on that myself.