Hi dhodg. Your story sounds SO familiar. My husband went through much of the same while married to his ex, right down to the drug abuse. He left her when their children were 1 and 3, and she got custody. Most N's are really good at putting on a normal, pleasant, well-adjusted face and lying to ANY one to get their way.
My advice to you is to visit
www.deltabravo.net where there is a wealth of information that you can use. It's mainly for non-custodial parents, but it gives tons of tips on what to do BEFORE you get a divorce, as well as a message board you should look through.
Going to the doctor for your own depression is a good idea, too. There may be an anti-depressant you can take for a little while to help reset your brain chemistry. Living with, and being abused by, an N for so long takes its toll on people mentally AND physically. I've heard it compared to post-traumatic stress disorder.
And you're not crazy, you're exhausted. You're doing everything and being everybody in your marriage (wife, husband, mother, father, housekeeper, doctor, chauffeur, etc.) You're getting no support whatsoever. But therapy is a great idea, just for you, to maybe help you learn some coping techniques you'll need whether you stay married to this woman or not.
Most important: take your time. Learn as much as you can about your chances of gaining custody. Get your emotions straightened out as best possible. Research attorneys in your area to find the best for divorce/custody litigation. Reconnect with your family; you'll need their support.
Hang in there!!!!!
-Heather