Hi there AustenJ, let me join
lighthouse9 in sending a warm hello.
This may be the only type of "relationship" a pwBPD has a chance of maintaining. None of us that had serious relationships with pwBPD had no idea what we were getting ourselves into... .but my buddy does... .he has no problem using her as she will most certainly want to use him. I recall a movie called Eyes Wide Open... .but I warn him that she sings the Siren's song very well, and her beauty and charms are very seductive... .I don't know if he will pursue it, but from my experience with her, I'm positive she will.
Hmm, i don't know about you. But i find this rather disturbing. I mean, your buddy... .is if i may, either, playing with fire, having a gross overestimation of his own ability and in extreme situations, possibly even displaying traits of being a narcissist? (without being rude). I mean, to have no qualms about using her and her using him, that is a stepup for a workable but obviously dysfunctional relationship. This "using" of each other is very much what i would deem as "objectification" of people. You no longer see this person as an individual but rather as an "object" to be used... .in most cases for your own personal gain or satisfaction and probably even sex in some situations. My own uBPDexGF was attached to a person displaying NPD traits and in that kind of relationship, it could last, but terribly abusive.
I would say that having BPD, the individual has alot of difficult maintaining relationships because of over-sensitivity and perhaps even the constant need for external validation ( ie being validated by another person ). That alone makes it difficult to communicate, and stop going through circular arguments. But i would say AustenJ, it is your friend's choice. The old saying holds. You can certainly bring a horse to the water, but you can't make it drink. Warning your friend is certainly kind of you, but he'll have to either take it from you, or learn it the hard way, or perhaps even... have some own issues if he continues to pursue this.
Yours,
Spero.