How much wine is too much wine?

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I know that different cultures view alcohol consumption differently, but how much wine do you consider too much wine? I have a friend who finishes a two liter bottle of wine just about every day. He drinks this while sitting by himself in his room playing video games. I think this is too much wine, especially since now that he lives with us, I cannot have an open bottle of wine for any reason without him drinking it. I used to keep a bottle of cheap red wine around for cooking with and now I can't because he willd rink it. I used to be able to share part of a bottle of wine with my husband and save the rest for another day, but now if there is an open bottle, the roommate drinks it. Am I worried for nothing? If it were your friend, what would you say or do?