My relationship took a turn for the worse about a year ago and my SO began leaving consistently until 4-5am, cheating, lying, etc. We are at the point where I have asked her to see a therapist or I am leaving and she refuses. I meet with my therapist weekly and she has said that from my side of the story, she feels strongly that my SO should be evaluated for BPD.  I want my family to stay together but i need her to seek some type of positive improvement and have heard the telling someone who may have BPD that they need help is not always the best idea. The following is an email i have prepared for her but am nervous to send. any advice on how to try to have her seek help would be very appreciated!

"Between research, forums, and reading on my own anxiety, I think there is a chance that you have Borderline Personality Disorder. The most successful treatment seems to be lifelong talk-therapy with someone who has experience with BPD. That's why i have pushed for therapy so much for you. It works like a roller coaster so the good times are great but they never last unless you seek help... which is why even though you have made me happy lately I still am afraid of just believing things are better... i cant handle another drop... I don't know much about BPD but a therapist would. 

It explains why you feel trapped and a need to run. why you cant do your work or give up at school, why you have depression symptoms and anxiety for no reason. It explains why you get so angry so quickly...this isn't like something that can go away with general health, or that can easily be medicated... its much different... 

I hope im wrong, and no pressure, just if you feel like it take a look:

https://www.psycom.net/depression.central.borderline.html"