I was in a similar position very recently. This was my second relationship with an alcoholic. The first one lasted 9 years, but the second one lasted only four months. This was because I had learned some lessons from the first, but just not quite enough to keep me from making the mistake of getting involved in the second. Now it's finally registered with me, and there won't be a third. Alcoholics have an overpowering compulsion to drink.
AA can help a lot if a person is committed to attending as many meetings as physically possible, surrounding themselves with people in recovery, and finding themselves a good sponsor whom they like and trust. They also need to be prepared to really really work hard on the 12 steps. Recovery must be the number one priority in their life. If they are swanning in and out of meetings and half-heartedly involved in the process, then they are either not ready to get well, or they don't understand the program. If it is the latter, they probably think AA, or the people in it, are going to work some miracle that will take away the inconvenience and disruption that alcohol is causing in their lives, allowing them to carry on as normal. This is not how it works!
For whatever reason (a disease, chemical imbalance, inner turmoil...who knows), along with the overpowering compulsion to drink comes the belief in the alcoholic's mind that drinking is the best possible thing for them to do at the time. They may feel that they have no other option, or that this time will be the last time, or whatever, but they make that choice because at that moment in time it is exactly want they want to do.
Can you imagine if you really really wanted to do something, and people requested that you didn't, tried to put obstacles in your way, tried to trick you out of it, monitored you 24/7 so that you couldn't, begged and nagged you not to, and threatened to leave you if you did (even though you knew they'd never do that because they obviously care too much about you)? It would be frustrating, and that's how I believe an alcoholic in active addiction sees those who are trying to get them to stop drinking. They just want people to butt out of their business and let them do what they want to do. They will use whatever means necessary to get you off their back, ie. lies, manipulation, guilt!
So this is where rock bottom comes in. It has been proven time and time again that it is only when a person loses everything and everyone (or, less often, just one thing that is important enough to them as everyone's rock bottom is different), that they begin to see the damage their choices are causing to their lives. It is only when things fall apart completely and the alcoholic is really ready to admit to themselves that they are powerless over alcohol and their life has become unmanageable, that they will get what they need from an AA meeting, accept gracefully the help they are being offered, and commit to the 12 Step program. In doing that they may get the tools they need to deal with their thoughts and compulsions in a different way - a way that doesn't result in them drinking.
Unfortunately, until such time, you need to work on understanding that you didn't cause it, you can't control it and you can't cure it. If you think it's in your own best interests to walk away, then muster up the strength to do so. If you choose to stay, then you need to practice the art of detachment if you are to find any peace of mind. You can find out about detachment at an al-anon meeting (but don't go there looking for advice - they don't give advice, just support and a friendly, non-judgemental ear!). I would also highly recommend Melody Beattie's Book, Co-Dependent No More.
I'm sorry this is so long, but I have had a few breakthroughs in understanding this lately, and I just what to share what i've learned. It's not easy, i've recently walked away and i'm still hurting, but i'm now concentrating on my thoughts, my feelings, my actions, my dreams, my future, my happiness, and it's proving to be difficult but a much more worthwhile venture!
Take care and good luck!