We can't change other people, they can barely change themselves - consider how many New Year's resolutions are made and broken shortly thereafter.
I was at first so shocked by the realisation that the alcoholic was lying to me, earlier in my marriage, that I tried to deny it to myself. He presents himself as the soul of honesty; I wanted so much for that to be true, that I tried to believe it when told that were I not the person I am, he wouldh't have to lie to protect himself. Twisted, alcoholic blaming, which awoke my guilt and caretaking behavior, but the truth, as an old AA guy once said, is that "The rocks in our heads, fit the holes in theirs."
I had to fight my way free of years of childhood indoctrination, before I could get to the place where I truly understood - what he does, he does because of who he is, not because of who I am. When I could finally let that shame go and accept, I could speak up about what it was really like to be married to him.
I could understand that there might, in some far future, be a chance of his changing, but I needed to deal with the here and now. When my friend died, so quickly after diagnosis, it was brought sharply home to me that if I wanted honesty, I had to give it to myself, I could wait forever for him to stop lying to me. I had to leave.
It's been six months, and it's been hard in ways I expected, and those I didn't, but I know it was the right choice. Even when my grief threatens to overwhelm me, I still know it was the right thing for me to do.
I thank my Higher Power for the friends who've supported and helped and encouraged me, old and new, and for the comfort given when it's all felt like too much, and I've only been able to say softly, "Oh, please help me."