Of course, I can't actually know what's going on with your wife, but we had a similar situation in my house. About eight or so years ago my husband suddenly stopped drinking. I was fine with that as I frequently stopped drinking for health and weight reasons and for me it was no big deal.
Like your wife, I assumed he was doing for health reasons as, like you, he never shared any deeper feelings or motivation. Abruptly, he changed. He became spookily quiet and very grouchy. If I could go back in time I would have been a lot more sympathetic and supportive, but I just didn't understand.
Finally, we went on vacation with friends and he started drinking again. I guess I'm telling you this because I can relate to your wife. You haven't shared with her your concerns about being alcohol-dependent. Is it possible that she would stop pushing drinks on you if she had the full picture?