It's not surprising you hadn't known more than Bi-polar. In decades past it was the go-to label to get therapy.
It appears that many people with acting-out Borderline traits (pwBPD) never get diagnosed. It has been noted that in past decades when there was little focused therapy available, most insurance would not cover BPD since it was viewed as incurable. So many therapists would instead diagnose Bi-polar, which expressed similar symptoms, instead since that therapy was covered.
Bi-polar is seen as a largely chemical or hormone imbalance and so its issues may be resolved with drugs. However, though BPD may be moderated with drugs, there is always a risk of the patient stopping the drugs. BPD is a Personality Disorder and the core issues are the person's own personality and warped perceptions, most often exhibited with excessive self-interest. So it is, to some extent, perceptions (with ever changing moods and feelings) versus reality (facts and documentation).
Cognitive or Dialectical Behavioral Therapy (DBT or CBT) have had the best results but outcomes will vary, of course.
But a diagnosis is not necessary for you to observe, conclude what you're dealing with and deal with things as they appear.
I first came here due to my growing marital discord. But I've come to recognize BPD patterns in others here and there. One is a sibling who I always considered grumpy. After my parents had both died, that sibling was given the option to decide the extent of his bequest. Sibling's delays held up the estate for a couple
years. Finally when the estate moved forward, that sibling was angry that his financial share hadn't arrived yet after a few
weeks. Was there any consideration for the other siblings who had to wait two years for their portions? No. Is it any wonder I haven't spoken since, nearly a decade now? Want to know who my next door neighbor is? Yeah, it's like that.

I let it go. There's a saying, Let Go and Let God.