The most simple answer is that you - as the partner - are never the one to tell them
https://bpdfamily.com/content/how-to-get-borderline-into-therapyProfessionals do not recommend that you tell a loved one that you suspect that they have Borderline Personality Disorder. We may think that our loved one will be grateful to have the disorder targeted and will rush into therapy to conquer their demons, but this usually doesn't happen. Instead, this is difficult advice to receive and more likely to sound critical and
shaming (e.g., you are defective) and incite
defensiveness, and break down the relationship trust. It's not like a broken leg where the affliction is tangible, the cure is tangible, and the stigma nonexistent. While we are grateful to learn about the disorder and the pathways to recovery - for us the information is validating and represents a potential solution to our family problems- to the afflicted, it is
shaming (you are defective), stigmatizing (mental illness in general, Borderline Personality Disorder specifically), and puts all the responsibility for the family problems on the loved one's shoulders.
