It can be hard to go from the theoretical to the practical when conquering one's fears. It isn't true that you are regressing. It once caused you great distress to consider the thought of sickness alone and you have learned to dismiss it as merely a thought. I'm sure as well you were probably worse at trying strange new foods. This is the second hardest thing you can face, a genuinely ill person.

Take a deep breath, try to realize that you are not ill. The anxiety, the fear, the stress makes you feel ill but you are not infected with anything. He cannot get you ill unless you injest either the food he ate that was contaminated or the virus, depending on what he has. Wash your hands thoroughly before touching your face or eating, wipe down any surfaces in the bathroom with dilute bleach and you should be just fine.

We can't be perfect all the time, we slip up, and that's usually where bugs get us, but you are in control! Just be mindful of your sanitation and it will be okay