I'm in the same situation. My SO hasn't left but it's the lying that has done the most damage. It'll take forever to gain trust back. But then again, the number of times I've lied shames me... Who would trust me?
Why do we do it? To protect our alcoholic self. Until we truly and honestly want to quit, we will do anything to protect our alcohol. We don't or didn't want to quit drinking. So we lie. Admit it or not, it becomes the most important thing in your life