Rainheart, my mother just recently died after a long bout with cancer, so your post particularly resonated with me.
My mother's last days were by far the most difficult period I ever had to face. What made it even more so that I was surrounded by family members who wanted nothing more than to pretend that she wasn't dying. Whatever unhealthy coping mechanisms they had were magnified one thousand times. The hospice nurse and I ended up being as thick as thieves because it was pure sheer insanity. She had seen it all so with me there was no judgment.
I am telling you this because I think your concerns are very much valid. I am also writing to you because I think your anger is a pretty healthy response to what you're enduring. I am also concerned that your husband may ask you to do things, such as purchase more alcohol for him, that you do not want to do, under the guise of "supporting him through this difficult time." I don't have any advice but I do have a story that you might find useful. [Trigger alert: Suicide request]
My own mother actually asked me to help her die at one point. I had made it very clear in the past that this was something I would not and could not do for my own personal reasons, so when she asked me again I had to tell her no. It tore my heart to say it but she replied by saying that she completely understood and respected my wishes, even though I could not fulfill hers. She also made it clear that she still knew that I still loved her.
You don't have to say yes or agree with somebody 100% of the time to love them. Anybody who expects otherwise is setting up that relationship for failure.
PS. I can count with one hand the number of times that I drank during my mom's last three months, and I never did it while I was "on watch." I was already sleep-deprived and I didn't want to stack the cards against me OR her by being drunk. There are much more healthy ways to cope, but I suspect you already know this.