Your at the right starting point.
Yes, her issues could have been acute and not BPD traits at all - or it could have been a laundry list of other things. When we encounter high conflict or destructive relationship behaviors it is important for us to know that the problems can be caused by a broad range of things that look a lot a like:
immaturity,
short term mental illness (e.g., depression),
substance induced illness (e.g., alcoholism),
a mood disorder (e.g., bipolar),
an anxiety disorder (e.g., PTSD),
a personality disorder (e.g., BPD, NPD, 8 others),
a neurodevelopmental disorder (e.g., ADHD, Aspergers), or
any combination of the above (i.e., co-morbidity).
How often is "any combination of the above?" In an NIH study of 34,653 people*, of those that had clinical BPD,
74% had another personalty disorder,
75% also had a mood disorder, and
74% also had an anxiety disorder.
*Laboratory of Epidemiology and Biometry, National Institutes of Health, Bethesda, MD
It often takes a professional a lot of time to sort through this - it will likely take you time, too.
And then there is you. What did you contribute? And yes, clingy codependent behavior contributes to bad relationship dynamics... .maybe even her loss of interest.
The way I sorted this was to profile her part - what was pathologic, what was normal relationship conflict, and what was driving her. I then turned those investigation skills on myself - polled my own inner critic.
It took many months and a few one-way alleys before I started putting my hands on it.
Have you read this? See yourself in any of it?
https://bpdfamily.com/content/codependency-codependent-relationships