@Shadow,
Welcome. You're in good company.
I know what you mean about fluctuating moods... that might be the perfect way to put it.
If you're looking for a sort of quick-start guide, one of the more universal lessons/exercises can be found here:
https://www.bpdfamily.com/content/communication-skills-dont-be-invalidating @AppeaseNoMore,
Great observation re: double standards. Reasonable or merely polite people often accept some degree of accountability because it's generally understood that disagreements of any kind require two people, and no single person is always 100% correct. This world just doesn't work that way. In this way, someone who insists that they are infallible is... obviously fallible.
In my experience, even when I readily accepted criticism, my uBPDxw would often say "you're just saying that to avoid the discussion" or "you don't really mean it" - etc.
If I responded with "OK, how can I give you some assurance?" my uBPDxw would often perceive a challenge rather than support.
I found that's where boundaries can come into play:
https://www.bpdfamily.com/content/setting-boundaries I hope some of this helpful.