Although there are various ways to experience and express spirituality, I think conditions that are other-centered ( people and objects like drugs, shopping, activities) ( PD's, co-dependency, addictions, drugs) are the antithesis of spirituality.
IMHO, a spiritual path involves developing a sense of purpose, self in relationship to others, a sense of connection to a larger purpose ( some people may choose one or more to consider: God, religion, nature, the cosmos- involving the question why am I here?). It involves looking at one's self.
People with PDs and codependency tend to look at others as a way to take away personal pain and for a sense of self. Spiritual people are concerned with others, and look inward and to a higher consciousness or their own sense of purpose when dealing with such issues as who am I?
I think we have all run into people who walk the talk and those who seem to just talk.
But spirituality also includes not taking assessment of someone else's spirituality. We can't possibly get a full picture of the heart and minds of another human. We can't know just how spiritual someone else is, PD or not. Their path is their's. It isn't our place to judge someone else's spirituality. IMHO, it's a big enough job to figure ourselves out.

Part of being in a relationship with someone with BPD is to understand what we can do and can't do about their behavior. Their choice of spiritual interest, or whether or not to continue therapy, or choice to use substances is not something we can control. The choices we have are with our own personal boundaries when it comes to their behavior. I know it is sad to see a friend make choices that we think are not good for them, but for something like therapy, they have to be motivated to do it.