It's also important when you love someone with kidney disease/kidney failure that you remain his fiancee and eventually his spouse, not his nurse or the "food police." You can be the extra pair of hands for his treatment after you both are trained, but hopefully he will learn how to do all aspects of his home HD treatment himself.
You say your fiance doesn't have the energy to work. How are his labs? How is his dialysis adequacy? If he's not getting enough dialysis, that could make him feel exhausted and have a poor appetite. Doing dialysis longer or more often can help people feel better. What is his hemoglobin and hematocrit. Anemia leads to fatigue, low energy and limited endurance. If his albumin is low, this is an indication that he's malnourished, which can happen when someone is new to dialysis, appetite is poor and food (especially meat) may taste funny. Hopefully as his body gets used to dialysis and especialy when he switches to home HD, he'll feel better physically.
How is he coping with kidney failure and dialysis? He could be depressed, which is very common when someone is new on dialysis. I've told people that it's common to grieve kidney failure just like you would a death of a loved one. He should have a social worker who can talk with him about his financial concerns, concerns about his job, his goals, his future. Also, having a loving fiancee (or spouse) can help someone come to terms with kidney failure easier.