I was diagnosed with Celiac Disease almost 2 years ago. I tend to not say anything about
it to people. The only time I will is if I have been invited to eat dinner at someone's house, then I will explain that I cannot have gluten and I will ask what was used for the dishes. But if I'm unsure about
anything, I just don't eat, or look for salad.
I have had to get agressive one time at a restaurant with the server. I ordered a hamburger without the bun and when my food came, there was bread crumbs all over the plate and the burger pattie. I sent it back, making sure he understood that bread could not even touch my plate. I did get the correct food the second time.
But for the most part I keep it to myself, unless someone asks me, then I will explain it. But I don't have an agressive personality anyway and would rather blend in with the paneling!! If I do eat out I don't demand that we only go to places where I can eat everything. As long as I have salad I'm good.
You may just give this person time to adjust to having to eat different. And maybe you may have to be upfront about not wanting to always talk about your health problems. Just say, "I go out to eat with my friends to have a good time, not to dredge up my health problems. I have plenty of time to think of that on my own."
Anyway, hope this helps.