Welcome sparkplug!
You sound like a thoughtful and intelligent person. First let me say that your weaknesses are not what you have to face. You are somply powerless over him and his disease. When I gave up the illusion that I had any power over what was happening to my loved ones I felt a huge feeling of relief.
You sound like you have a pretty good handle on what is happening...his dishonesty is shame. He can't face what he is doing so he has to lie and decieve. And there is no reason for you to believe him.
I am going to suggest you head on over to the Alanon forum on this site and go to the power posts at the top. There is some excellant reading there. Also get a copy of Melody Beattie's "Codependent No More" It is great reading and you may see yourself those pages.
About leaving...my thoughts on this subject are that I choose to not do anything until I am sure. By waiting I will not have to look back and wonder. You can stay in the relationship for today and change your mind tomorrow. As those today's pass you can learn and grow and then make a decision with confidence.
I am an Anon...I look forward to seeing you on the Anon forum.
Hugs,
JT