I am in a relationship and have been for over 4 years with my partner. I have read non stop about BPD and she fits the criteria, but I always question this and keep searching as I need more evidence! Is this common?
Yes... .very common. You want to understand what you are facing in the relationship. There is usually a thought that if you just understood it well enough, you could explain it to your pwBPD... .they would see the light and the issue would be "fixed".
I also used to think that if I could "just" get her diagnosed, all would be better... .magically... .somehow.
I think you are wise to focus on symptoms, because that is what you actually see and can respond to. Hopefully we can help you have healthier responses.
FF