It's hard, no doubt... maybe the hardest thing to go through, seeing someone you love being destroyed when you know there's a way out because you're sober.
After I sobered up my dad kept drinking and getting sicker and my mom and me and others were at our wits end like you... I thought that Alanon's advice and the pages in the AA Big Book on working with others didn't apply because no one knew how I felt... It turned out many had been through the same roller coaster.
My dad is 79 and just passed one year without a drink. Miracles do happen and he stopped when he could... All I had to do was to not get dragged into the insanity and the suggestions of others helped...
You probably know about Alanon, but here's a link to their home page:
http://www.al-anon.org Real meetings with people and online rooms and like this one helped too. My mom also got a counselor at the local drug and alcohol center.