I always feel weird about taking food from other people's houses. I get so self-conscious about not being entitled that I always refuse everything, even if I want something. But I recently learned that it's good manners to accept a drink, etc. from your host if they offer it to you. It makes them feel better about their hosting abilities, and it puts them at ease. Then they're not wondering if they don't have the right thing for you, or if you think you're better than what they're offering. So even though it seems polite to refuse, it's better form to accept. How bout that?
But there is of course a line that you need to be careful about not crossing. A line that this Redditor's boyfriend definitely crossed. I get that you want your partner to be an extension of you, but maybe food is where we set a boundary.