This is essentially what has happened with two married family members. It has been going on for well over 30 years. The self confessed male alcoholic in the marriage has ostensibly stopped drinking (this has happened several times in the past 3 years but he had continued drinking under cover) and the female partner has merrily carried on drinking at a high level throughout providing little if not no support. This is incredibly frustrating, as when they met 30 years ago, she did not drink at all. Both have severe chronic health problems, some relating to alcohol abuse. They both have enabled each other massively over the years.
Any advise appreciated. Particularly how to support the person who is trying to give up. It is my personal feeling that if you love and support your partner and are concerned about them you should be trying to stop drinking at least in their presence. But I speak that as a non-alcoholic.