Hi IndoorGardener and welcome to the BPD family!
I’ve been married for 15 years and I am very sure my spouse has BPD. He doesn’t seem very receptive to therapy but things are getting worse. He never seems happy anymore and he is on meds for depression and he got mood stabilizers in the last year. But honestly he seems worse since the mood stabilizers.
Is the doctor who prescribed the mood stabilizer aware of BPD? I'm asking because there are a few medications that are discouraged for BPD patients, such as benzodiazepines. And there is no drug that's approved to treat BPD itself.
It seems like he hasn't been diagnosed yet. My wife was recently diagnosed, and that helps a lot. But it takes a very good therapist with whom the patient has a high level of synergy/connection. The patient must seek the diagnosis spontaneously.