I think sometimes, when we are hit by addiction, be it our own or others, it makes us super aware and highly sensitive of others bad habits. That maybe drinking too much, pills or drugs.
I think also, once you have been dragged into addiction and the chaos it causes, you are always fearing it may happen again be it with the original addict or another falling prey to the disease.
That said, if it makes you unhappy, it makes you unhappy.
You seem to be under a tremendous amount of pressure at the moment. You also seem to be looking after and worrying about so many other family members - your sister, your son and your mum. Not that you can change any of what is going on.
Perhaps its time to look after yourself a bit more maybe? Get some early nights, soak in the tub, do your nails, read a book, telephone friends etc etc. Anything for you.
I think also you could bring up your husbands drinking at the alanon meetings but in a non judgmental or angry way. Perhaps saying what has happened with your son has shaken you to the core and that you despise what alcohol and drugs can do to a person and that you don't want them causing misery to anymore of your family or those you love. Perhaps that might strike a chord with him.
Take lots of care
xx