Hi SheAskedForABreak,
As far as what want. I want someone who wants to help me when I say I am upset, not a person who runs and tells me she "needs time" to process even the simplest request. I want a person who wants to grow together, not someone who expects me to "fit in" to her vision of the world. I want a partner.
BPD is like riding an emotional roller coaster, an intense struggle with emotional regulation that can be hard for us to imagine. Her intense feelings shift quickly and rapidly and make cognitive distortions likely, followed by impulsive behaviors, sometimes even psychosis during severe distress.
With my BPD loved one, I notice too that competence in one area does not necessarily mean competence in another area. A lot of people with BPD regulate their emotions externally, so if the environment is invalidating, they feel invalidated. If the environment is validating, they feel validated. Validation helps them regulate emotions.
This puts the burden of emotional maturity on our shoulders. We can expect more when we do it in tandem with them. That means learning some skills and working on our own emotional reactivity, plus having support from others who understand what it's like to be in these relationships.
It's not easy work. It's also rewarding, and the skills apply to any and all relationships, not just BPD.