Hi @Sane74
Welcome to the forum
You probably read my comments in the original thread so wont bore you with the details again but wanted to connect with you and am happy to help where I can where you have any specific questions. My wife (18 years) suffers from BPD and is at the moment going through a particularly rough time.
I can understand your feelings of frustration and failure in not being able to help, I have often felt like a failure when things go badly for my wife, especially at the moment as my wife is currently in hospital after a meltdown and I feel I should (/could) have done more to prevent it.
The reality is though we can only be responsible for our own actions (or so everyone keeps telling me). This is still something I constantly struggle with though as I feel responsible for creating a safe environment that enables my wife to remain well.
I have found that how I react to a situation can effect the outcome, so what I am working on (with the assistance of counselling) is instead of being upset about how my wife is coping (or not) and trying to amend her behavior or fix things for her, to focus on how I am responding to the situation and my behaviour. (I have 18 years of bad habits to break here).
The other thing that I have to work on is to understand sometimes my wife just needs me to listen to her problems and not necessarily provide a solution or fix things for her.
I also agree about what you said about the boundaries, definatly easier said than done.
This one is tricky as it can easily be interpreted as controlling behaviour. It is important however to be clear about what is acceptable behaviour. It is much easier to set boundaries early than regaining them later, something I am findind at the moment.
I hope I have been of some help. Please feel free to ask any specific questions that you may have.