Hi gojira,
I'm sorry you're struggling today. I get what it's like when what happens in a pwBPD's life spills over and impacts ours - even if we had nothing to do with the situation.
You have a good insight here:
My wife is devastated. She recognizes that she fell into her same patterns and made the same mistakes (this isn't the first time this has happened). There's a part of me that wants to reach out to this person and ask for forgiveness, but I suspect that's the codependent in me. At the same time, I don't know how to help my wife and break this cycle. She has a psychiatrist but refuses to see him on a regular basis and BPD has never been given as a diagnosis.
You care about your W and of course you wish she weren't in pain. We hurt, too, when our loved ones are in pain and devastated.
There can be a middle ground between "well, it's her problem, so I really don't care" and "she needs me to fix it for her".
Many communication approaches for challenging people include empathy as a component. Empathizing doesn't mean agreeing that she is right, solving her problem for her, accepting blame, telling her what to do/what she should have done, or rolling over/being passive. True empathy is about accepting that she is feeling the way she is feeling in the moment, and putting yourself in her shoes: if you felt X, what would that be like for you?
Can you think of a time when you did something that tanked a friendship, and then think of how you felt? That is something you can bring to empathetic listening -- which may be the most supportive and loving thing you can do for her, much more so than rescuing or fixing.
"That would feel devastating to have that happen in a friendship."
"It makes sense that you'd feel [guilty, overwhelmed, panicky, etc] after what happened -- I've felt that too."
"Anyone would feel that way after what you've been through, and I respect that you want to make things right."
"I just want to be here to listen to you, babe... How do you think you want to move forward with this?"
...
Has she initiated any conversations with you about how she feels?