Hello Forum
Just confirm I meant Borderline Personality Disorder by BPD. @canc

It appears to me that the core symptom of BPD and its subtypes is always emotional dysregulation, (including strong emotions and rapidly changing emotions)
For a BPD diagnosis, it is not essential to have abandonment and engulfment concerns, but they are very common.
When I initially wrote my post, I wrongly thought abandonment and engulfment concerns were always present in BPD.
My friend with BPD for many years is very impulsive and did get very angry with me once.
I am aware of Bipolar 1 and 2 the old name Manic depression, but that is not their condition.

Unfortunately, I have felt let done by my friend at times.
I think it is their over-enthusiasm that misleads/confuses me.