I also dated a borderline, possibly two. I definitely had a long distance frendship with one that ended terribly when allowed her to move in with me platonically, or she might have been an absolute psychopath. SWhen I spotted the BDP, I moved out for three months until she finally left my apartment. Re the first one, I wrote a poem and short personal essay titled Twisted Relationships, Tanka of stormy rollercoaster relationships with a borderline. Here's the tanka portion, you won't need to read the essay portion to understand:
You are the greatest
You’re disgusting I hate you
Wait please don’t leave me
Thrives sowing chaos around
Rollercoaster ride from hell
If anyone wants to read the explanation: https://medium.com/know-thyself-heal-thyself/twisted-relationships-6c148e17f0d8