If you read about the traits and recognize yourself in them you may want to look for a place that will actually diagnose you. I am on meds for my mood (an antidepressant, mood stabilizer and antipsychotic). Moods are also treated by DBT. There are a lot of resources online but I find it best to get DBT from individual or group therapy.

The best ways you can be a good girlfriend are to get treatment and be self-aware. My relationship of 12 years ended because of my emotional dysregulation and it was only after that I found out it was BPD all along. I'm trying to work on recognizing negative thoughts and moods for what they are and not isolating, self-harming, raging etc.