Fried foods/fast foods are really hard on me as well. The grease, the high fat content, and the seasonings all seem to affect me. I go to KFC rarely, and I only get the mashed potatoes when I do go there. And even those are full of additives and chemicals that I probably shouldn't be eating. Generally speaking, I rarely go out to eat and cook most of my meals at home so that I know what's going into them.
I know there's a such thing as oven baked "fried" chicken (it's battered similarly to fried chicken, but it's oven baked so it's less greasy and fatty). You might want to google some recipes for that and try to make it at home, that might be easier on him than KFC. Baked chicken is a pretty safe food for most of us.
Your boyfriend might also want to keep a food diary so that he can figure out specifically what foods/ingredients are bothering him. I did that for quite awhile myself - I journaled everything that I ate, what symptoms I was having, how much pain I was in and how many bowel movements and their consistency, etc. That allowed me to correlate symptoms to certain foods or ingredients (for example, I figured out that garlic is a trigger food for me).
