Hi there, novembercharlie,
Glad you found us, you are welcome here!
You're in a difficult spot, but in many ways it gives you a good place to operate from. Many, if not most, of the members here, myself included, struggled with relationships of various sorts with people who are not diagnosed at all. While getting or having a diagnosis is not some magical cure-all, it can be helpful. Here is a resource for people with BPD that you may want to consider sharing with your person:
www.bpdresources.net/As for you and how you will deal with it, please have a look at the banner here on the right. There are a lot of good tips and lessons on managing conflict and taking care of yourself. That is your primary responsibility, by the way, novembercharlie: to take care of yourself.
A relationship with a pwBPD makes some pretty big demands on us to be centered and wise, patient and consistent, empathetic and resourceful. It is ok to see and feel for another's pain, but many of us did so at the cost of our own mental and even physical health. Stay aware.
Can you say more about the "major impending life changes" that have caused things to go out of control? How long had you been together before things turned?