hi kitkat,
id urge you to do a search on this forum for some very similar threads.
a long distance relationship with a person with BPD is different than living with them, for sure. doesnt necessarily mean the outcome is different. there are always variables. it could be shorter, it could be longer.
i havent had one myself, but from what ive read, while youd be inclined to think about the abandonment issues, a long distance relationship helps mitigate the engulfment issues. it does not mean your partner is cheating on you.
I agree with "once removed". I'm coming out from a medium-distance relationship (250km apart) that lasted 1.5 years and ended just before New Year.
We saw each other each weekend (we stayed toghether from Friday evening to Monday morning usually), but we also had the chance the live togheter day and night for few "blocks" of times (each one lasted around 3-4 weeks) for a total of around 3-4 months out of 1.5 years of relationship. So I both experienced the "distanced" part and the "living togheter" part.
From what I saw, on one hand the distance helps to mitigate the engulfment (in my case, I noticed remarkably less drama, fights, etc.). So, the distance may help A LOT in prolongating the relationship and defer some inevitable issues.
On the other hand, especially towards the final months of the relationship where I got devalued little by little, she sometimes told me she felt alone (but we anyway had lots of fights in that period, so probably it was all part of the BPD cycle).