Hi colorfysunshine,
Welcome back
I think it's common for those of us in BPD relationships to get pulled down to the lowest skill level, especially if we had difficult family of origins where we were exposed to similar behaviors.
PTSD, depression, anxiety would probably make you even more susceptible. It takes a lot of strength to not be emotionally injured by someone with BPD. The key is to raise the skill-level and that can requires effort and commitment to change.
What happens when you both push each other's buttons?