Hi SOTC,
So sorry to hear your mother has cancer; it is hard seeing people you love suffer. My aunt, who just turned 80, did well when she received chemo and radiation for breast cancer a few years ago. I went through radiation as a teenager (stage 2b) and my experience was that sometimes it was harder for loved ones who felt powerless.
I think it is pretty common to have multiple “failed” attempts when getting sober. I did it over and over again. Don’t beat yourself up; you have a drive to stay sober, that constant, nagging addictive voice will dissipate the more practice you have. You also seem forthright and that honesty and self-reflection will take you far.
Best wishes to you during this difficult time.