Hello Andigo
I feel for you, friend. 22 years is a long time to not know which end is up in a relationship. It can really mess with your sense of who you are. The utter confusion in a BPD relationship, not to mention the emotional roller coaster you have likely been on, can be profound.
You are wise to recognize your own self care comes first. And like you said, you have to be there for the kids.
When you try to do something that is about your own self-care, what happens? Is there a healthy activity within reach, that can become a goal you set for yourself?
How young are the kids? I imagine you have to work around their schedules?