Hi there, Pops26
Really, you are not alone in this. If you browse a little, you'll find thousands of situations like yours. I have two kids (11 and 6) and their mother has BPD, we suspect the kids have also important emotional chalenges. I've been told about ending the relationship every 10 days since it began, maybe once a month since the diagnosis for BPD was accepted. Yesterday was the last, so far. Today she texted me that she's having such strong feelings for me it hurts her, yesterday she told me it was over. So... .You are not alone.
The diagnosis takes some months to settle. It's a huge blow, and depending what she has heard about BPD it can be devastating, it has a really bad reputation, and anyone wouldn't like to be called that. But in time it can help a lot. Specific treatment is essential, as other treatments can be damaging instead of helping. Be sure to reinforce that she sticks to treatment even as it is very hard for her to go.
We cover the same issues over and over again, it helps to talk about it and to be understood. Take you time to browse through the website, the lessons the basic tools, maybe look for a recomended book... .There is a lot to learn that makes things better, and give us some solid ground to feel less lost.
We have our own circle of emotions, feeling that if the relationship ended we would somehow rest, and we wouldn't care as much as years/months ago, gives us some guilt feeling that goes on top of a lot of negative feelings. We need to take care of ourselves, and in our case, of the kids too.
People with BPD more than anything feel different and alone. So the biggest basic need is to feel understood and to be told they are valid. They need new, concious tools to manage their emotions so they don't grow out of control.
Best of luck.