Even when I injured my back and was limping with my leg, she saw going to the hospital with me and supporting me through my pain as a burden. She told me, “I didn’t sign up for this.” When I asked about why the business was being run so poorly, she said it was because she did not want to do hard work.
This is probably a most honest statement. She says she didn't sign up for anything difficult, she doesn't want to do it. I like the quote from Maya Angelou "When someone shows you who they are, believe them"
But you know that this isn't real life- there are good and easy things, and there are those that take effort, and that her wish, to not do anything that takes work, isn't realistic. It may work when someone else is carrying that for her- but even so, the other person is human too and may have their own limits to how much they do that.
Which is why I think she also won't want to do the work of parenting over time. Young children are more easily controlled and compliant. Older kids can be challenging, even well behaved ones assert their autonomy. Children also are a source of great happiness too- but they require time and caretaking- something that doesn't seem to suit your ex. You've seen this already.
My BPD mother was similar to your ex in that she couldn't manage the work of day to day tasks, which included parenting. Other people stepped in and did this. While it seemed odd to me at the time that she wasn't doing the things I saw other mothers do, I am now grateful for that. If your ex is near her family, it's possible they are stepping in to help- and that could be a good thing. Not everyone in a family has BPD and it's possible they are more competent.
I saw something similar to what happened when you hurt yourself with my father, who had been her enabler/caretaker. PwBPD perceive themselves as victims, and so other people in their world are either rescuers (helpers to them) and if they are not- they are persecutors (hurting them) (look up Karpman triangle).
When my father got ill in his elder years, he wasn't able to keep up the level of caretaking/enabling. He also needed care at the time. This was a "reversal" of the usual dynamics between them. While one would expect understanding and empathy for a spouse in this situation, the opposite happened.
This doesn't exuse it- but it hopefully will help you to see this as not as personal to you. Underneath this refusal to help, this cold, cruel, veneer, is a very disturbed person, someone overcome with their own emotional distress.
You've found this out now, and now you can rebuild your life and I encourage you to do so. You are not responsible for your ex's feelings and you didn't cause her BPD. If she's already seeking someone to date- it's due to her own emotional need for someone to be an emotional caretaker to her, not about you. That person may be idealized at first- but will also experience the same person you did.
Don't try to figure her out- it's not possible to know all that someone else is thinking or feeling. I think refocususing on rebuilding your life is a good thing- for you and also for your children. I agree with FD to consult an attorney about your parenting rights. You may be tight on funds at the moment but it's worth the cost of the consultation to know what to do. If there are parenting classes, anger management classes that are required for unification- it is in your favor to do them as having completed them will stand as evidence.
I know you are scared for your children but I think consulting an attorney will give you a solid path to follow to regain your rights. I think FD makes a good point that sooner is better than later.