Save your cheat meal/s for the week until your around her. And just because you go out to eat, doesnt mean you cant eat healthy. Everything in moderation, she orders desert, have one bite, ect.

I had the same problem with my ex, although she would constantly ask for nutrition advice, and then ignore it.

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I don't do this for my family, my friends, women, accolades, pride, or ego. I do it for me and no one else, its just part of who I am.