Hi Birdy28,
I highly recommend Al-anon. I am the child of an alcoholic father (sober 29 years now), a recovering alcoholic (sober 16 years) and the partner of a DH who has an alcoholic DM (still drinking and slowly going mad). Alcoholism exacts a terrible toll on everyone who comes into contact with it and many people do not realise they need as much help as the actual drinker. I know it sounds odd but often, very slowly and insidiously people who live around alcoholics develop behaviours which make them as dysfunctional as the drinker and certainly as unhappy.
The misery, feelings of powerlessness and attempts to control the alcoholics behaviour would drive even the most reasonable person to despair so Al-anon recommends turning our focus away from trying to change that situation and focussing on what we need to change in ourselves to make us happier and more comfortable. You may already be aware that no amount of begging, pleading, threatening or whatever it is you have tried will stop your DM from drinking so it is a waste of time and that will drive you mad.
Alcoholism is an illness, one that tells the sufferer that they do not have it. That their drinking is reasonable and that other people are just interfering. It's like being bonkers, all the evidence points to a problem but the alcoholic is on such a state of denial that they cannot/will not face it. Coupled with a physical reaction to alcohol that almost forces them to drink it's a potent combination. Underneath all of that is a load of other emotional/psychological/spiritual stuff that can be worked out over time but requires the alcoholic to stop drinking first. It's a viscious cycle and one that can only be broken by the alcoholic.
I know the disease concept of alcoholism isn't everyones way of thinking about it but certainly helped me understand my behavour and that of my father and took some of the blame and anger out of it all. It does not mean I am not accountable for my behaviour but it helped me see that I was not just a horrible person who drank too much I was in fact quite unwell. However, I would not have changed if people had continued supporting my drinking and bad behaviour and was grateful when people withdrew from me. I then discovered that I had to do something about my life rather than expecting other people to do it for me.
Al-anon meetings usually follow a format in which someone will share their experience and what they did to help themself get better. They may talk about the literature they use, the 12 Step program which is key to recovery and you will even hear talk of God. Try not to be afraid of the term, many people in AA and Al-anon have a very broad view of religion and spiritual beliefs and it does not mean you will have to become religious in any way. I certainly use spiritual practices (mostly Buddhist) as a way to help deal with my own life but don't subscribe to a religion.
I hope this has helped a little and am happy to tell you more if need be but the best bet is to try a few meetings and see how you get on. You may hate it in which case you could try counselling or therapy or you may find a place that helps you feel a little less despairing and who knows maybe even happy and accepting of your situation as you learn new ways to cope with it.
Good luck.