If you're in a relationship with someone who presents traits of BPD, is there a way to have conversation about it that doesn't backfire?

Obviously, I'm not a qualified psychologist but I can imagine there are members here who have somehow helped a loved one get a diagnosis.

My partner has been attending therapy, off and on since April. As it turns out, he is focusing his attention on how I'm unable to meet his needs. His therapists (sounds like he's changed them) advise him to spend more one to one time with me, without our toddlers. At this point, I'm pretty reluctant to because of some hardship he's caused within our family (compulsive lying, financial infidelity, covert abuse, and over the top covert reactions).

How do you get someone like this to get assessed for a possible dx if their main goal is to protect their personal image?