hey,

Unfortunately, what you have experienced is par for the course when dealing with a person who has BPD. I've experienced exactly what you have, and have things go from great to horrible to okay to great in such a short amount of time. And you are right, it is draining. Extremely draining.
You have found the right place. I am glad you have set and stuck with a few boundaries. That's a tough thing to do, and I struggle with this myself. I know that continually pacifying them is not the answer. I've tried, and it worked for awhile until the goalposts kept getting moved farther and farther away until I was exhausted.