Borderline is the existence of extremes in us that we cannot tolerate at once (hence "dialectical" in DBT). People can't be good and bad at the same time. That's why we fluctuate btwn idealizing and devaluing people. We have an extreme need, an attachment to people, but we also have an extreme fear of abandonment and rejection. Both cannot exist at the same time for us, so we cycle btwn "I love you, I hate you, please don't leave me".

If you think you have BPD, were you an emotionally sensitive child? Did you experience childhood trauma? Both are early indicators of BPD. Do either of your parents suffer from mental illness? It's a theory that narcissistic parents have BPD children. Are you emotionally regressed for your age? Do you feel like a child trapped inside of an adults body? It's often described that way. Do you split people into good and bad? Do you have a fear of rejection and abandonment? Do you tend to get attached to people?

There are over 200 varieties of BPD. BPD is similar to PTSD and BP. And if you're a teenager/young adult, these symptoms might be normal for the stage of life you're in.

I wouldn't go diagnosing yourself. BPD is not something you hope to be diagnosed with. If you want to be diagnosed, seek a professional's opinion.