Hi Miss at a loss,
Thank you so much for posting on this forum. These are impossibly difficult situations, and unfortunately I don't think there are simple answers or solutions.
The one thing I believe is essential, is to put your own mental health and wellbeing first. This can feel impossible if you're empathetic, or feel intense emotions of shame or guilt about the state of the person you love. You can even feel, with certainty, that the 'right' thing to do is chase the person you love doggedly down the path they're on, no matter the cost. But there's a whole world out there that needs your attention.
When I was young, my mum had many mental and physical health problems and addictions. While I was far from a perfect child/teen, as I got older I tried to be a passable son, comforting Mum when she was self-destructive, and doing what I could to manage and improve our situation. Ultimately this was unsuccessful. My mum, and my whole family, just got worse and worse, to the point that I moved interstate in my early 20s to escape the horror of it all.
I'd receive harrowing phone calls from Mum back home, and unannounced visits at my doorstep interstate. I was so tormented by shame and guilt, I would attempt to solve her problems remotely from interstate. These attempts were also unsuccessful.
Over time, I have come to the view that partners, close friends and family, are often particularly ill-suited to helping a person recover from these types of issues. I think partners, friends and family often have intense emotional connections, have experienced shared traumas, and act from patterns of behaviour developed over years, that are hard to adapt to new realities.
I am now extremely cautious about how I interact with my Mum, and there have been years where I have chosen to have no contact with her at all. I have given up completely trying to provide emotional support for her mental or physical health issues. There are professionals and societies that do this better, and more sustainably, than I can.
Setting tough boundaries with my Mum was the hardest thing I've ever had to do, and I felt like Satan for doing it. But for us it was the right call. Gradually, Mum became much more proactive engaging with professionals and societies, and building long term strategies to improve her situation. Her wellbeing, and that of our whole family, dramatically improved.
I hope the above helps in some way. Please feel free to keep posting. All the best