I had a similar operation four years ago. The surgery went well, and I was discharged after ten days. Eating was both trial, and error at first, and just small quantities. The major problem I had was finding good diabetes care, and help. Like your husband my blood glucose levels varied between hypos as low as. 2.7, and hyperspace into the 20’s, and off the scale.
I was going to the GP almost weekly, and nobody could seem to help. I kept asking to do a DAPHNE course, but initially told that there wasn’t one in my area. Then told that there was one, but the waiting list was over a year. Eventually I found a course which was not too far away, and the waiting list was around six months. It was the turning point. To know how to deal with problems that occur with diabetes instead of blindly trying to control my highs, and lows was great. After the course, and because type 3 is so difficult to control, my consultant suggested that I had a pump, and sensor. This has enabled me to have an almost normal life again. It’s a full time job dealing with my fluctuating glucose levels, but the pump whilst having some idiosyncrasies has been wonderful.
As far as carbohydrates are concerned, personally I have found that having a low carb diet has definitely helped.
I assume your husband is also having to take creons with every meal to help digest his food.
Bottom line is persevere to do a DAPNE course. Make sure you are seen by a diabetes consultant, and Give yourself time to adjust to the surgery, the diabetes, and your diet.