There is a step in AA where you try to make amends and forgiveness. This is an important step because so much emotional feelings of shame and guilt is associated with the behaviour of drinking.
My AH is doing the AA program and a lot of his drinking has been triggered by his emotional relationship with his mother. He hasn't got to the step of trying to make amends with his mother but this is something that he eventually will need to do to find a peaceful place since his mother is such an important part of his life....but also has the power to cause such emotional and painful feelings to arise. Again, knowing his mother...she isn't the type of person that will give him the emotional warmth and comfort he needs if and when he gets to that step with her.
It seems that your husband understands that his ex wife holds a lot of power on his past and present emotions which contributed to negative feelings inside that propelled him to drink. Your husband was married to her for 15 years. She touched his life immensely over those years whether it was mainly negatively or not. He needs to find a way to let go of all that anger and negative feelings so that he can find more peace and happiness in himself.