Hi Es_Valentine and

I came from a similar situation as you: I only began to be aware of my uBPD mother's disorder after a lengthy dysfunctional relationship with an uBPDgf.
Anyway, we've had lots of recycling. I'd ask to talk things through, we'd talk for a bit, he would provide in excruciating detail all the things I did wrong, I would frantically offer to fix them, he'd make vague noises about maybe, we'd go on romantic evenings, and then immediately afterwards he would say he needed "space." It got so bad, that at one point we had gone out and had a nice dinner, and he blocked me from contacting him.
As children of borderlines, I think we are conditioned to take the "emotional fall" in conflicts because that is the only way we've learned to salvage our relationships. So when our BPD loved ones, blame us, we accept the blame as a default. And perhaps sometimes try to reason with them in the hopes of changing their hurtful behavior.
What I've come to realize is that our BPD loved ones often don't want to change and prefer to believe that we are the ones who are broken, because this is the limit of what they can emotionally accept. People with BPD (pwBPD) exhibit "splitting" behavior, also known as black and white thinking. That is, they either idealize or devalue people. To them, you are either perfect, or else you are worthless, with no in between. Sometimes they will alternate between their idealization and devaluation so much that it confuses us non's and we end up subscribing only to one or the other perspective (while living with the cognitive dissonance of the other).
So your ex would "provide in excruciating detail all the things [you] did wrong" because he was devaluing you at the time. But also, by making you the emotional scapegoat of what was wrong in your (both of you) relationship, he can absolve himself of any fault. Because if he did associate some fault with himself, then he might end up devaluing himself as well; the "splitting" applies to their self perception as well -- they must see themselves as faultless and perfect, or else they will hate themselves as being worthless.
As a child of a pwBPD, I well understand the desire to "fix" our loved ones (perhaps by fixing the relationship). For many years, I kept selecting partners who were in a sense, incapable of providing the love I wanted for myself. And I see this as an surrogate for the major issue I have which is to try to "fix" my mother (and father) so that they would love me in the way that I've always wanted to be loved. But the bitter truth I had/have to accept is that my mother (and father) are incapable of loving me that way. On the bright side, as an adult, I am now capable of providing myself that which I couldn't get as a child... . still it is a recovery process.
You might consider, that your exBPDbf kept pushing you away to get "space" because what triggers his dysfunction is when someone gets to close, becomes too intimate or familial to him. If he suffers from BPD, then when you get that close, he becomes overwhelmed by the irrational fear that you will inexplicably abandon him. And the "best" way to avoid abandonment, is to be the person who abandons. They leave us before we can leave them (even though we never had any intention of leaving).
Unbelievably, this has continued to happen and after the last time (in March), I found out I was pregnant. Because he blocked me, I had to have my best-friend get in touch with him to notify him. He immediately sent me an angry text demanding proof. I offered to show him the tests and have him come to the doctor's appointment with me. He refused. Which led to another series of discussions on why he couldn't have a relationship with me and how he wanted to cut off all contact if I had a miscarriage.
I would argue that each time he has "abandoned" you (for a time) and only to return later as if all the fault of his leaving belongs to you, each time this happens, you become more attached to him in a powerful but powerful dysfunctional manner. Some describe this attachment as "trauma bonding," others see it as "Stockholm's syndrome." But each time he hurts you gravely, when you choose to accept him again, you are doubling down on your attachment to him. To more you recycle him, the harder you are making it to ultimately let go of him.
Your miscarriage, his behavior in the aftermath of your miscarriage, the grief you probably are still coming to terms with from the miscarriage, these are all mini-traumas, stressors that will make it very difficult to detach from your BPD loved one. I hope this helps you understand why you are having difficulty with your rational decision making.
You are in the right place.
Best wishes, Schwing