I would say it's your bpd causing much of the inability of letting it go. Are you in treatment for it? If not I would advise you to find a T (Therapist) to help you learn ways to let someone go, and manage better in life so that bpd doesn't negatively effect your next relationship.

Certainly you do need to cut all ties, yes, you need to stop watching him online, it's just causing you more problems, Therapy can help you process it all.

Welcome to PC