I guess you'll just have to tell him again, and add if you didn't already, that:

You feel like it affecting your relationship (not just that she stresses you out), and it bothers you that you have to fight for time for your own husband. She has other family members too, that attempt, right? He is not responsible for her alone, no one should have to do that by themselves, nor give up their own life for that person.

I mean, it's not as if he signed up to be her home care and babysitter. I understand depression, but also that I cannot expect one single person to always do everything for me, and I try to share bits with other close people.

He is going to have to realize one day he really will have to choose---and he will probably become resentful to his mother anyway, I think, if he has to give his own life up.

However, if you start seeing him even less, and almost hardly at all and tell him you are feeling lonely and really need him and he still won't understand his own priorities as the only person who can provide intimacy with his partner (His mother's is to get her act together), I guess you have to make the difficult choice.

While it is true our parents matter, they are our elders, and, she isn't old enough to actually require help of the younger generation yet, and it's not fair to her children to lose their futures because of her alcoholism.