I just want to start this out by saying that I have experience with exactly what you are talking about, being in a relationship with an alcoholic, and I got out. I walked away.
But not until I had given this man 16 years of my life, and so much more...
For me, it took the birth of my son to finally push me over the edge. I had hoped that our son's presence in the world would be enough of a reason for him to want to get into recovery, so I allowed him some time to come to this realization, but sadly, he didn't. Oh, he loved his son to the ends of the earth, but the addiction and the mental illness that went with it was just too strong. So I left him. I was/am so afraid for my son, in that he may already be genetically predisposed to deal with the afflictions his father deals with, so I sure wasn't going to stick around and also let him LEARN how to be an alcoholic from his father, like his father learned from his. It had to stop, so I stopped it.
Throughout our relationship, I often reflected on why I stayed with this man, and for me, it wasn't about my self-esteem, I had/have plenty. I know my worth. And it wasn't even about the roller coaster, where we'd have these euphoric times, then bottom out... our relationship was never in the euphoria phase... it was generally pretty rough, to ridiculous. So why did I stay? I could not abandon him. I truly believed he needed me, that I was the best thing in his life, and without me, he had absolutely nothing. And in large part, this was true. But what was also true was that I was enabling him by staying. I was inadvertantly allowing his behavior to continue because I stayed, and I kept things together. So yes, codependency definitely had it's claws in me. The guilt I felt for potentially abandoning him outweighed any potential damage I was doing to myself, or anything I was giving up by staying.
But thank God for my son, because he is the singular reason I found the strength to do the absolute hardest thing I've ever done in my life to date. Walk.away. I finally felt responsible to someone more than I felt toward my ex. My ex was an adult making choices. My son needed me to be strong for him. So I was. It was agonizing, but I vowed to be the mother that my son needed.
In the aftermath of me leaving, my ex bottomed out, and due to some really poor judgement resulting from his alcoholism, he ended up spending some time away. And while that experience was excrutiating for everyone involved (including me, as I still do love this man as a friend and the father of my child - like family), it was the absolute necessary catalyst to bring him around to recovery, which brings us current.
My son finally has the father he deserves. A sober, dedicated, attentive, loving man who would hand his life over for his son. I knew he was in there, but he was just buried beneath all the muck.
In some ways, I feel bad that I waited so long to leave, because I can more clearly see how my staying perpetuated the situation. I'm not blaming myself for his behavior, I know his choices were solely his. I wish recovery had come much sooner, but I am so abundantly thankful that at least it came. I know that relapse is possible, if not probable, but I am choosing to be cautiously optimistic... and if/when it happens, well, we'll deal with that chapter the best way we know how, with the added knowledge and insight that these last few years have allowed us.
So that's my story. I've been there. And I'm ecstatic to say that I've made it through to the other side. But I wouldn't have made it if it weren't for my son. He's my reason. He's my everything.