Thanks guys I really appreciate all the comments, some great motivation in there.
I can't believe I had been missing the answer for so long. Sometimes it's hard to see the most obvious stuff but as soon as I realised alcohol was having a huge impact on my depression and was in all likekhood the single most contributory cause I suddenly woke up. If I give up alcohol it's going to make a massive difference to my depression? That for me was the turning point, my defining 'Why'. Depression for me is so debilitating and I'd go as far to say it's as bad if not worse than alcoholism. When I have good days I can feel on top of the world, like I can accomplish anything and that how I want to feel everyday. Depression holds me back and alcohol fuels my illness. My 'why' is to choose life.