Why do some pwBPD insist on getting married very early in a relationship and others fear any type of long term commitment? My ex would never have married me. She even made a statement "why can't we just always be together without getting married?"
The fear of engulfment and the fear of abandonment operate on the same pendulum with BPD. An unstable sense of self sometimes can be seen as "marry me so I exist" or "marry me and I fail to exist". This pendulum can swing back and forth as the sense of self fluctuates. It isn't rational, it is BPD.