I was married to a semi-diagnosed borderline for 3 years. It was a fusion of exquisite Heaven and tormenting Hell, with regular battles through purgatory on the way. Semi-diagnosed, as we worked together and separately for 18 months with an integrative psychotherapist, who made a provisional diagnosis without the necessary DSM-V tests as my wife refused - the therapist referred her to a psychiatrist specialising in Schema Therapy and DBT for testing and treatment, which was refused as I am "the one with the problem". The therapist was kicked to the curb, as were the other two therapists who were "siding with me due to my lies".
Don't go to joint therapy or counselling with them. They may suggest it, but their reason is to create a blame exercise to vindicate themselves. The therapist will be triangulated as best your partner can do to gang up against you. It will make things inestimably worse. The therapist will see through the lies within dozen sessions, but by then the damage will have been done.
Sadly, we have young children together. We moved to Asia from Europe to be together for a fresh start, and after I left the family home again this year as I could take no more of the appalling behaviour, she bolted back to her native Russia, abducting my children, without even telling me. I haven't seen my beloved kids in months and I've been totally broken, although now starting to recover somewhat. She's in touch now and again with torrents of blame, which I mostly ignore. The main thing aiding my recovery is being away from the abuse, and seeing more and more normal and healthy interactions between healthy couples. My wife is mesmerisingly beautiful physically, and highly intelligent and educated, but she cannot hold a job down nor indeed live in the same place for longer than a few months at a time. She is a true lost soul due to her condition. I do not hate her, and I never will. I forgive her, although I hate what she did to me, our children, and our extended families.
Women with BPD will rip everything meaningful and wholesome in their lives to shreds, and cause the lives of you, your children, your family and possibly even friends to fall into the most egregious, fruitless, and totally pointless chaos. They will do it time and time again, for no reason that makes any sense to you or outside observers. The destructive power of their disorder knows no boundaries, and it will never change without years of treatment and a willingness to change on their part, which only a fraction of them are prepared to face up to. As others have pointed out, they base their decisions and memories on emotions rather than logic. To argue with them about anything is pointless. It will go round and round in circles and they will argue about the same topic until they collapse in exhaustion. They genuinely create false memories and narratives in their heads: they are rarely consciously lying, and this is the most dangerous aspect of the condition. Depending on their comorbidities, I believe that many BPDs are sincere in their emotions and feelings, they can feel love, and they can want the best things and to do well, but simply don't have the emotional capability to not destroy. Their labile emotions will trump logic, reason, empathy - every single time.
No matter how much you give a BPB, things which any sane woman would do anything within their power to protect (in our case, an incredible luxury lifestyle in Singapore, and an ever-present, faithful and loving father and husband trying to create a peaceful environment), their emotional tsunami will regularly escalate small disagreements into life-shattering conflicts until everyone is in shock, reeling, mentally razed, and sobbing in the smoking wreckage of their lives. After that, they will argue and blame some more. Once the pattern starts, it will happen with ever increasing frequency, near weekly. It will never cease, it will only lie dormant sometimes. Police, social services, courts, and other authorities are very likely to be involved. If that happens, you may be bankrupted by legal fees from cases they have started that they cannot possibly afford, and they will do this from an indignant, strident sense of self-righteousness. If they start multiple legal actions, they will change lawyers multiple times as their lawyers cannot cope with their bottomless demands, and they will possibly leave a trail of unpaid bills in their wake. They will never compromise.
In our case, 30+ physically violent acts in 3 years, resulting in multiple hospitalisations due to injury, were not even the worst of the legacy of the marriage.
As for me, I got through with my sanity, job and prospects intact but it was teetering on the brink for a while. I financially support my kids even at 5000 miles difference, and I know they will come back to me one day, and I will know them, even if it's a decade or more. I no longer love or pine for my wife herself, although I hold fond memories of the person she can be at her best, and I wish her a happy life if she find the introspection needed to make a change one day. I do dream of hearing healing words from her one day - "I hurt you, I am sorry", but I accept it's very unlikely. I'm not sure how long it would take me to truly allow romantic love into my life again, but I am sure it will happen one day. Explaining all of what happened to a new partner will be a difficult thing to do.