I'm a lying drunkard, so I'm leaving my wife of 20 years because I can't undo what I've done
Are you leaving only because of your drinking?
It's because of my drinking and my lying habits
I'm sorry you had a lot of problems, but you've been with your wife for that long. I'm sure she would understand with a good discussion, and it's irrational to want to just throw it all away. You need to work through this and not run away.
I know it's irrational to run away from problems
Then you'll stay and try to fix things. That's great! Just be honest with your wife, and I'll bet she'll be open to patching things up.