It is very difficult to trust people that are addicted to alcohol/drugs. They will look you right in the eye and tell you that they are clean and that they are ready to overcome their addiction and will do whatever they must do in order to stay with you. They will beg for your forgiveness and tell you that they have learned their lesson this time and will never drink/use again. It's a vicious cycle.
I recently left someone addicted to alcohol/drugs, so on some level I can relate to you. It was a short-term relationship and I got out early. I can only imagine the barriers and struggles you face with your husband though. How long have you been married? I'm sure you love him dearly and it's very difficult for you to leave him. It is very challenging to stick with your ultimatum you gave him; stop drinking or I'm divorcing you. I would seek out as much support as possible from family and friends and talk about your decision to divorce him. Maybe with the help of a trusted friend or family member, you will gain the courage to divorce him and move on with your life. I would also suggest to make a list of all of the reasons why you want a divorce and make another list of the benefits you will gain by leaving him.