Gosh, can you work up the courage to say, "Please don't comment about my habits right now. I'm working through some stuff "? I know it's easier said than done but this guy is being a judgmental spoodyhead. At least this way you aren't accusing him of being part of the problem.

It sounds like a therapist who specializes in eating disorders is a good fit for you. There might be an underlying cause beyond That Guy and you need to get to the root.