Oh, sweetie... doesn't he know that since it's a diverticulosis issue that Immodium is NOT going to work? He has to stop taking the Immodium because it isn't doing any good to begin with. None of those OTC anti-diarrhea meds are going to work. They're just not. No Pepto, nothing.
He HAS TO give his stomach, intestines, and colon time to heal. I was hospitalized for five days due to a particularly bad diver attack and was lucky not to require surgery. Your husband is VERY lucky that he's alive. Most people who have what he has DO NOT feel the pain. The pain is the only warning sign we have, really, that we need to make changes in our diet or that there's something wrong and we need to head to the emergency room. Some people will get the infection and die never feeling a thing. So he HAS TO take this seriously. His body is telling him to change how he's eating and he HAS TO listen to it.
First and foremost he has to find a new gastroenterologist. One that won't tell your husband to "live with it." He's already had one surgery. He also needs a nutritionist that's familiar with IBS and diverticulitis/diverticulosis and other inflammatory bowel diseases.
Until then you can do this in order to give his digestive system a break: Start him on a Clear Liquid Diet for three days. He would be able to have teas, broths, juices, flavored bottled water, anything liquid that would be clear at room temperature, Jell-O, etc.
After he does that, he can go to a Soft Foods Diet. Cream of Wheat, mashed potatoes, and other foods that don't need to be chewed much if at all. I'd go at least three days on that, probably four days or as long as he'll tolerate.
Drink lots and lots of fluids but avoid milk and carbonated drinks. Avoid coffee. Avoid creamers.
Get him on a Low Residue Diet. He's going to need to eat foods that are easy to digest, and THAT means that he needs to eat foods that might typically be off many diets because of the carbs and he'd need to avoid foods that would be considered very healthy for others but unhealthy for him. Make sure that vegetables are steamed. Skins are peeled.
It's EXTREMELY important to avoid seeds like poppy seeds, corn, popcorn, whole unrefined grains, sesame seeds, tomato seeds, cucumber seeds, strawberry and raspberry seeds, sunflower and pumpkin seeds, peanuts, nuts, nut butters, peanut butter... as a general rule. I can't eat any of things ever without getting the telltale searing cramps and diarrhea a couple of days later. Popcorn is what landed me in the hospital and while I may have cheated and had a strawberry here and there, I haven't touched popcorn since my hospital stay two years ago.
With Lactose Intolerance, if he's still drinking regular milk and eating regular cheese then that could account for much of the diarrhea. There are many substitutions he can have as long as he doesn't also have a milk protein allergy. Lactose-free milk tastes exactly the same as regular milk and is, in fact, still cow's milk. They simply remove the lactose ie. the milk sugar because it can't be digested (your husband is missing lactase enzyme in his large intestine required to digest the lactose). You can cook with lactose-free milk exactly the same way as with regular milk EXCEPT FOR making the pudding in the boxed mixes. You'll have to make pudding homemade using cornstarch. You'll have to make certain things from scratch to avoid milk products but make them using lactose-free subs at home. In many instances you just have to make an ingredient change without any hassle.
He can have Kraft shredded mozzarella and other Kraft cheeses as long as they say 0 grams of lactose in the nutrition area on the back. Cabot and Cracker Barrel also cater to Lactose Intolerant customers, so look for 0 grams of lactose on packages.
Look for the ingredients lists. Avoid things that have milk, milk powder, caseinate, lactate, lactylate, loaf meats, salami, pepperoni, and other cured sausages. No milk fat, no butterfat as ingredients. There's now Yoplait lactose free yogurt, although many people with lactose intolerance can have regular yogurt as long as it has live active cultures in it.
Avoid McDonald's and other fried foods... a lot of times, the frying process converts sugars or there are hidden milk products in the fast food items. My daughter can't have fast food fries anywhere because of the lactose issues.
If you have any questions, my PM box is open. :-)