Distraction. Do other things you enjoy without her. Hang out with other people and don't talk about her. Do your laundry
Distraction is a DBT skill as well, and DBT helps people with BPD.
Are you dating this person? That wasn't clear to me from your post. If you aren't, try Checking the Facts, another DBT skill. If you are, again, try distraction as well as Self Soothing and Improving the Moment. All DBT skills that you can google if you have no idea what I'm talking about