Borderline. Many sessions will i need?

Its appreciable that you are willing for therapy (many don't admit their problem). Then you must also be knowing that Borderline PD or Emotionally unstable PD is a condition which has strong biological basis involving multiple neurotransmitters, neural circuitry (like most other psychiatric illnesses). If symptoms cause dysfunction, sole psychotherapy (dielectic behaviour therapy) won't suffice. Medicines modulate the neurotransmitters and neural pathways....and enhance or quicken the psychotherapeutic effect. Also medicines help the client cope better in crisis moments.  Psychotherapy is gold standard for borderline PD....but then its time consuming....and the number of sessions depend on symptom severity and has individual variation. Consult a clinical psychologist who after assessing the symptomatology would be able to guide you regarding sessions.