Sounds like he's not open to discussion on it. We live in a world where we're surrounded by people's addictions: sugar, coffee, alcohol. It's hard. I'm glad you get to vent here. Sounds like he's proctecting his addiction. When people are in that place it's hard to talk to them. It sounds like, from what I heard from you so far, that you should just believe in yourself and try to work around him and the coffee, though it is hard. Keep going in your direction without opposing. Best. Hugs!
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"Me voici donc seul sur la terre, n'ayant plus de frère de prochain d'ami de société que moi-même." Jean-Jacques Rousseau
"Do not think, 'I am alone.'" Sasaki Roshi
WonderWoman