Thank you both for your input. Boundaries is something I work hard on in all areas of my life, with him it seems to be a struggle.
To answer your question, the impending birth of our second child was his reason for finally telling me. I have a feeling his world was caving in on him though. In retrospect I was questioning him more and more and I think he got sick of the lying to some extent.
He is currently at one of his CA meetings. He goes to about 3 per week, has a sponsor now and continues to work with the professionals to get his Meds right.
Part of my motivation to give him these chances are because I want to tell my kids that I did all I could to keep our family intact. When I first found out I made the decision to give him a year to turn things around. I understand that getting and staying sober is a huge struggle and I question if leaving now would be giving up to soon.