I can't guess with 100% certainty, but from my own experience things that are said like that are nothing more than saying what a pwBPD wants you to hear. They may actually believe it as they say it, but as my therapist reminded me ad nauseum, actions speak louder than words. My ex told me repeatedly how he knew how his rages affected me, agreed to leave the home when/if he had one and began the pursuit of getting therapy, including intake with a mental health organization, getting assessed and signed up for DBT, taking CBT, getting a referral to a psychiatrist and an anger management. But, in the end, it was a ruse, designed to keep me around. A mutual friend who was also in the CBT class told me how disturbing it was to see him saying all the right things in class, but it was clear he wasn't taking it in to a level to make it stick. She spent some time with him outside the class several times having coffee and discussing it and she always felt he repeated the words he heard but never really understood what it meant. And the minute I told him I was done, he quit everything.
I'm not sure at all myself if they are actually calculating in their words and actions, or it's just a reaction to a short lived thought in their minds. I still have contact with my ex I am able to look at her words and actions more objectively. I originally was leaning my thoughts that they are calculating and just say what you want to hear, it's all a ruse. Their words and actions sure appear to be manipulating and calculated as if an evil person planned things to do that would hurt you immensely, they would do the same things that pwBPD's do.
Now that I'm able to look objectively at my ex, I'm starting to change my thinking. Yesterday I saw my ex, and what I saw was a very confused person and full of hurt and pain. I can actually see the internal struggles. On one hand she feels a lot of love for me but she equates the love with ultimate pain and then needs to push me away. When the push stage comes, they are capable of brutal words and horrific actions. When the pull stage comes, she can look very vulnerable which appeals to my caretaker personality, and appear to really love me. So I'm thinking that when they say things, at that moment they really do mean it. Their thoughts are just not consistent like a normal persons are.
I believe her thoughts on love are due to her childhood of an abusive mother and a father she loved and trusted so much as her savior in that situation. He eventually divorced, remarried and broke off all contact with her as a child. I can see how she equates love with an ultimate ending of abandonment and immense pain, thus the push stage.
Ultimately does it really matter in regards to our decision of being in a relationship with them is if their behavior is calculating, manipulating and purely intended evil, or if it's just an emotional dysfunction, (words or actions of the moment) that will be repeated over and over again causing us immense pain, and destroying our lives and chance for true happiness. If it's due to an embedded emotional dysfunction, it's not just going to go away. Either way the results and outcome is the same. Even if they express a desire for help, the only possible chance for some success is therapy, DBT specifically and even with that the chances are slim it will have limited benefit at best.
That's what I've come to grips with myself. I respect and owe it to myself not to get back in a relationship like that.