celestialvisionz, the difficult situation you've shared has brought back memories of my mother's bout with cancer. This is just another perspective on the ethical question based on my experience.
In the late summer of 2000, my mother was diagnosed with lung cancer (she never smoked). There was a tumor encroaching around her pulmonary aorta making it inoperable. After she was diagnosed, my oldest sister and I put together our knowledge of alternative cancer cures and supplements. My older sis could be very persuasive and my Mom was a good patient and took them.... or so we thought. After she passed three months later, my sister took care of going through her place to pack things up, etc. and found little stashes of supplements everywhere; in between cushions, in the back of drawers, anywhere she thought they wouldn't be found.
She had a heart of gold and I'm sure she stopped taking the supplements and began hiding them because she didn't want to hurt our feelings or our efforts to help; they were also probably uncomfortable to keep down.
While we felt we had done everything we could to help her win the battle, we were unaware of the tormented life she was living. Having gotten remarried 18 years prior to her illness, we had suspicions of her husband being kind of creepy, controlling, opinionated and insecure, but this wasn't confirmed until after she passed away.
He had a knack for making my mother feel grateful for him marrying her, saying things like "I don't know how aaaany man (my father) could leave such a woooonderful woman...". I was appalled the first time I had heard this, which was probably at least six years after my parents' divorce, and a few years after she remarried. Plenty of time to heal, yet he wasn't letting her. They were married for 18 years and I recall him saying that to her in front of us at least a half a dozen times, leaving her either in tears or in a uncharacteristic sadness every time. No telling how many times this was repeated in front of other family and friends.
Afterwards, I couldn't help think a psychological wound manifested as a life robbing tumor, a wound not allowed to heal because a knife kept being stabbed into her kind heart. She passed on right before Thanksgiving at a Florida hospital, 1000 miles away from her husband; she didn't want him around her and wanted to die in peace.
After what I've learned since then, I've grown deeply humbled by her unwavering courage to face death with her heart in tact.
I thought compelled to share my experience with you not to suggest something this sinister may be at work, but what I came to understand since then, and that is: we don't know what is written on another soul or what burdens the heart carries, nor how much resilience one has to heal these matters from this life or previous ones.
The best we can do is to help anyway we can... when asked.
Hopefully, your BF can find a way to help his mother proceed with grace and dignity, even if that means finding understanding and acceptance of her decisions.
