What do I do?

I'm a 36 year old man next week. My wife and I have been married for nine years this coming march.We have a 12 year old son. My wife is an alcoholic/ addict, and has spent the better part of the last nine years intoxicated. We fight about her drinking and sometimes she'll take off for a day or more on a bender. Sometimes on these benders she'll resort back to drug use. Today for an example she didn't come home from last night, school was cancelled, and I had to start making phone calls at 5:45 a.m. for a babysitter. She also has issues with anxiety, depression, social phobias, and suffers from to spinal diseases. She stopped working just prior to our wedding to have time with our son, but she spent the whole first 1 1/2 years drinking a 12 pack of beer and a pint of blackberry brandy. She becomes beligerant, moody, and unpredictable when she drinks. When she drinks she'll start at 7 or 8 in the morning and go till 9-2 that night. She'll drink this way every day for six months or more at a time. When she stops drinking it usually doesn't last but a week or two. on a reaaly good stretch she'll go 3-6 months, but that is very rare. All this drinking and she mixes it with scripts and sometimes even worse. She's applied for disability but was turned down based on my income. I have consulted with attorneys regarding divorce. They all seem to agree that custody of my son being given to me should not be an issue, this of course is my #1 concern.