What is the least painful way for someone with borderline personality disorder to leave their significant other?

If there is a: strong reason for leaving the signant other - than stay focused on the reason that you are leaving. Take care.

DBT skills: Making the decision to leave your partner is difficult and likely to be hurtful, even if it's the right decision for you. Have you explored DBT? Initially designed for BPD, but there are so many powerful lessons we can all use in our lives (especially during a break-up). Look up a DBT self help book, or a therapist that can help teach you the skills through individual or group therapy.