Oh, Snafu, horrible situation to be in.
Beety posted about this (her situation concerned drink) a while back.
I do honestly believe that sometimes the best and only thing to do is the hand-washing, and have done it.
One of my past v significant relationships was with someone who became more and more out of control in every area of his life through drink, drugs and general irresponsible behaviour. Like having two children, with a 4 month age-gap, DURING his supposed relationship with me. Don't get me wrong - we had a fantastic relationship. He is responsible for and the inspiration behind what I consider the best moments of my career development. He was / is a fantastic person. BUT he had been damaged by childhood experiences, and I relaised, evetually, that there was a dynamic which went:
'You don't love me!'
'Yes, I do. I really love you'
'You don't REALLY love me, look what I've done - now you'll walk away!'
'No I won't, I love you' we'll sort it out'
'You can't REALLY love me, I've done something unredeemabel this time, i'm such a w**r and i'm so sorry i've ruined our relationship'
And so on. he did it to hismelf as well as me. He just couldn't protect himself or his life. I realised that my (genuine) love wasn't enough - he had to find a way to love himself, and my continued attempts to make my love enough were just driving him to a more destructive 'proof' that he was unlovable, and he was strting to do things that did seriously comprmise my life.
So I went.
He isn't better, he isn't much worse, but he has hooked up with people who make him feel better / justified by being in the same, or worse state than him.
You can do what you can do, but if it isn't working, you can't do more. And if it is addiction, or something that just isn't being addressed, you aren't helping by being the pair of tights that enables them to put off the day they have to call in the garage to replace the fan belt.