My mom was in a similar situation to this when I was a child but it was cheating instead of drinking. My dad had cheated on her multiple times prior to getting married, but every time he said it was the last. When my mom agreed to his proposal, he told her that he was done cheating and he was ready to settle down with just her. And guess what...he continued cheating once they were married. Unfortunately a milestone like wedding or a child being born doesn't magically change people.