Thank you for writing. I understand why you are concerned. The reason that most mental health professionals hesitate to diagnose a 14-year-old like you with Borderline Personality Disorder is that, as you pointed out, the teen years are a time of enormous physiological change and self-discovery. In the process, the behaviors of some teens can look like the symptoms of BPD. That doesn’t mean it isn’t possible to have Borderline Personality Disorder as an adolescent. But it does make it less likely that it is the cause of the “symptoms” (emotional dysregulation, unstable relationships, etc.).
The person to talk to is your therapist. Therapists can’t work effectively if there isn’t enough trust for a client to share everything that is troubling to them. Do explain to your therapist that there are issues you are hesitant to discuss and why. I hope you will work it through so your therapist can be maximally helpful to you.
I wish you well.