It doesn't matter the quantity you drink. Some alcoholics need a drink everyday whereas others just drink once a month but get really wasted.
Many also become alcoholics due to trauma such as loss of a loved one or in your case-your marriage to calm your nerves. Usually alcoholics suffer from some form of depression. My AH uses alcohol everyday to self regulate his emotions and escape his feelings of anxiety, despair, work stresses, marriage stressed etc. But alcoholism is progressive. When once upon a time it was a glass of wine a night, leads to two and then now a bottle. Your tolerance has increased over the year to try to achieve the same calming effects of alcohol.
The path to sobriety means making a drastic lifestyle change for the better, that includes your marriage as your husband is a major trigger in wanting to drink.
I can understand your ex's stance on not wanting his son to be in the midst of an abusive home. Your priority should be your son and being fully present for him. Drinking a bottle of wine a day is not giving your son 100% of your emotional availability at a crucial point in his life.