Step one: get your own therapist, if you can afford it... caring for a loved one who is experiencing mental ill health is HARD, & you may need advice & support along the way.

Step 2: seek out lived experience wherever you can, as you've done here. There's a wealth of information to be gained from people with a lived experience of mental ill health themselves, & the people who love them. Just be aware that there are a lot of hurt people out there, among family & loved ones of people with BPD, particularly, so you may come across venom here & there from people who are hurting pretty bad after relationship breakdowns, etc. Try to read around that stuff... seek out compassionate perspectives instead - here are some suggestions:
- NEA-BPD's free Family Connections Program: The Family Connections Program | National Education Alliance for Borderline Personality Disorder
- Project Air for Personality Disorders Fact Sheets, particularly those in the Families, Partners, & Carers section: Fact sheets - University of Wollongong – UOW
- Author Bon Dobbs' books & his website, based on his experiences of having several loved ones with BPD: Anything to Stop the Pain – Help for partners and parents of people with Borderline Personality Disorder – Non-BPDs by Bon Dobbs

Step 3: diagnosis isn't necessarily the be-all & end-all... seeking assistance, in an effort to improve one's life is sometimes better than seeking a diagnosis, per se, unless said diagnosis is necessary for insurance or similar. Consider the potential negatives, as well as any positives, to attaining one first, as some people regret being diagnosed due to the negative impact it had on their relationships, employment, healthcare, etc.

All the best...

Cheers,

Fern