I'd like to welcome you here to the forum too. I'm glad Sophie_ M was able to point you to another who has a similar situation.
I do not have BPD and so cannot really know all that you have to try to cope with. I think Sophie asked an important question in what you find the most difficult and struggle with.
While I suspect we could well understand some of the things you are going though it might be better if you could spell them out, I don't want to either guess or insult you with generalities.
I do know that having hope built up by her going to residential care facilities 3 times, and then having her come home prematurely must seem so discouraging, as if there is no answer. One can look at it another way perhaps, each visit has laid a bit of groundwork, things that can be built on later. Familiarity with therapy might be one of these .
Have you discussed with her - from her point of view, what it was made her leave each time?
You sound at the end of your tether, and I'm wondering what support is available for you? Do you have partner, family or a friend who you can talk to and who will understand and care. Is there anyone you can have step in at a difficult time and allow you time out?
There will be organizations that specifically cater to the needs of the parents of those with BPD, I'm hesitant to cite any as I'm not familiar with them. I do know having others in the same situation you can talk with would be a hopeful avenue for your own welfare.
Can I suggest you ring our 24/7 Help Line on 1300 22 4636 and ask which organizations might be best for your area?
You are welcome to talk here anytime.