All I do is defend myself from untruths. Now I feel like i have added to this treatment or even caused it as I have lied to her or not told her things that would make her upset. All usually to avoid conflict. All that said I have admitted to her everythign that I lied about in the past on multiple occasions. How ever I have never admited to cheating or afairs as thats never reality. No matter what i say or do or admit I always lie.
As you point out, it doesn't work, so dont do it. We have a saying here JADE
J=Justify
A=Argue
D=Defend
E-Explain
Once you slip into this mode you are on the back foot and becoming more and more insecure. A pwBPD soothes themselves by projection, they have insecurities and the deal with them by passing them on to you. This is done by accusing and provoking those close to them. If you join in the issue you validate it as normal and worthwhile. Putting you on the back foot by pushing you into JADE puts them back on top, and more in control. It is part of their soothing mechanism. It is not necessarily deliberate, but is just an instinctive coping tool.
Try to avoid repeatedly defending yourself against the same old stuff. A simple we've been through this before and i dont want to go there again is enough. Reassure you them that you love them, but avoid tying it to that particular issue. Otherwise raising that issue becomes a way to obtain reassurance. It is all insecurity based