thinking about what you missed in the past is one of the paths back to drinking.
I've found it so much more productive to start thinking about happy times or things that are beautiful, a sunset, fall leaves, a beautiful woman. Staying positive and in the present will train your brain to be happy.
When I started I would wake up every day and just be happy I was alive despite the condition of the rest of my life. My list grows everyday and it is easier and easier to put myself in a positive mood.
It works, you just have to stick with it and honestly be grateful for every little breath of life.