Welcome Caboose: I'm sorry you are having trouble with your partner. Telling someone you think they have BPD generally doesn't go well. The best thing you can do is to deal with the specific problems.
These arguments became more frequent, lasting longer and longer, and I began saying, "You are arguing AT me. I'm not really participating because I have no idea what the argument is about.
Check out the links below. The information should be helpful in regard to the arguments. It generally takes two to carry on an argument. If you set some boundaries, take a time out and don't engage in circular arguments, it can make things better for you. If she keeps arguing with herself, you have to remove yourself from the situation.
BOUNDARIESARGUING - DON'T ENGAGE DON'T JADE (Justify, Argue, Defend or Explain) and avoid circular arguments TAKING A TIME OUT You can't change her. The only thing you have power over is yourself. You can control how you interact with her and how you react to her. Give the above strategy a try and let us know how it goes. There are links to more lessons in the right-hand margin. Take it a step at a time. Sometimes, when one person in the relationship can make some changes towards using an emotionally intelligent strategy, it can make a difference (even if the other person is still being emotionally immature ).