Hi
@Jan71 and welcome to the forum. I was diagnosed with type 1 in my 40s, and like your husband I had lost a lot of weight, I was underweight and looked awful! Within a few days of going on insulin I felt wonderful!
Please don't worry, you should soon have your old husband back now he is on insulin, as others have said. There is a lot to take in at first but in time it will all become second nature. There is no need to worry about what he eats if he has type 1 - it's type 2s who need to be careful what they eat and cut down on carbs. Type 1s can eat pretty much anything we like and just adjust the insulin to fit around the food (at first the hospital diabetes team should help with adjusting insulin doses, but after a while your husband should be taught to do this himself).
It sounds as though the person you spoke to on the helpline was being careful in case your husband turns out to have type 2, as dairy and nuts are good foods for type 2s who need to put on weight, but if your husband has type 1 he will be able to eat carbs as well - in fact he should eat exactly what he'd normally eat for now, so that the diabetes team can help him fit the insulin around his normal diet.
The only food/drink he should avoid are the things we'd use to treat low blood sugar (hypos) - eg fruit juice, glucose tablets, jelly babies, full-fat coke. He should have plenty of hypo treatments with him everywhere he goes though, so that he can treat a hypo immediately he has one, but not consume them unless hypo.
I hope he's been given a blood sugar meter (finger-pricking device) as well as the sensor and app, as the sensors are not always accurate at the lower and higher ends, so if he gets any odd readings he should always test with a meter to be sure.