Nici,
This must be so hard for you. Take it one day at a time and don't try to have all the big answers today. Maybe you can set a time of day to visit your father when you know he doesn't drink. Maybe coffee in the morning when he wakes up. It's not giving up on him to realize that you can't help him.
It does leave us feeling sad and helpless though. That's when we need to try and change our focus and get our minds on healthier things.
Make your days the best days you can. You will never be able to get these days back again. Try not to waste them on worry. It takes a lot of effort to pull ourselves out of this despair. The more you do it the easier it becomes.
Try to have some fun.
Hugs,
MG