I got diagnosed with depression recently but I doubt it’s BPD. I am willing to take it up with my therapist but first I want to understand a few basics.
How do I differentiate between feeling upset when someone leaves you (or abandons you) and abandonment issues for a person with BPD.
The term abandonment issues gets thrown around so easily that it’s difficult to understand what it’s really like to feel it. 
For me it triggers a depressive episode where making it out of bed gets difficult. I sleep through the day and stay up entire night scrolling mindlessly on my phone. The lack of energy is persistent. (This happened recently and when i read about BPD it all kind of came together)