Hi Hydroman,
suicide attempts are on of the hardest things we face. You are feeling abandoned and betrayed and understandably so. While some suicides can be seen coming many are well hidden or particularly with BPD are not so fully planned and have a strong impulsive component to it.
I had found a good psychiatrist, good therapist, my wife was in a DBT class, now I am dissolussioned. In my new job, its further away so longer commute and less flexability (no telework). I have to trust her and put responsibility for her safety, care, taking meds on her. She needs to tell me if something isn't right or she is in a bad way and obviously, that isn't happening.
You are working hard on your side and you are working hard to support her. Turning a relationship around that has been moving into the wrong direction for a long time takes considerable time. Don't blame yourself!