Chances of developing a new food allergy as an adult? Not allergic to anything I know of, but terrified of developing a new allergy. Afraid to eat!

Can happen. Although the incidence of food allergy in adults is much less than in children it can happen. The most common food in my experience for adults to become allergic to is one or more of the crustaceans such as shrimp, crab or lobster. If you are concerned about a possible food allergy you might want to see an allergist. All in all, I think your risks are minimal and should not stop you from eating.
Eat. You can develop allergies at other ages than childhood especially during times of inflammation in the gut. The gut becomes leaky to allergic proteins which the body's immune system may respond to. You can get allergy tested by an allergy specialist so you are aware of what foods to avoid when you are not feeling well (like a viral gastroenteritis).