I'd like to politely disagree with the posters who are pointing out that in situations like this there is often another woman involved. On the whole, that statement is probably true, but in this case I thing there's a good chance it's not.
I live with a man who was finally diagnosed with severe depression for most of his adult life. It took him into his 40s, and several stays in rehab, and an almost final stay in ICU before someone finally diagnosed the problem. Like many suffering from depression he spent much of his life self-medicating with alcohol, which led to a years-long battle with alcoholism. Thankfully, he has been medicated (and sober) for three years now and he is truly a different man, living a different life. Some of the things the OP has said remind me strongly of my husband in his pre-medication days.
Sugarbaby - I am glad to hear he is going to a doctor. If there is any possibility that you can lift your focus off the topic of divorce and the marriage for now, and focus on his getting diagnosed and possibly finding a solution, that would be my suggestion for now. Yes, your marriage needs work, and I think you getting couseling is a wonderful idea. (Been there, did that, it helped me understand a lot of things about the situation) but there is the hopeful possibility that his getting medical help will make dealing with your other problems easier. If you have the time and the space to just allow him to get well first, that may be your best path. I know how hard it is to put aside the relationship problems and give him the time he needs, but if he is making a true effort to get help, he deserves the time to do that, and you deserve the chance that you will be dealing with him at his best, not his worst, when you start to look at your marriage. Waiting is HARD - I know, I waited 5 years. Fortunately we were not yet married and it was easier for me to step back when things got to a really bad point. But once he was properly diagnosed all the waiting became worthwhile. It is truly amazing what today's medication can do for some people, when used under the proper conditions.
I wish you luck. It's not an easy path, but there is hope.
Linda