Does he have a hobby? Sometimes introducing new avenues to explore within the hobby may just be a way to help, but one thing I will say is that when a person is stressed, they like to cling onto what is familiar rather then trying to cling onto what is not. It is a natural thing to do. For example, if I go somewhere where I know I am going to have anxiety, I bring along a comfort item like a book about model railways. I just hold it and look again at the same pictures I have seen hundreds of times before. I may only read a tiny bit as just looking at something familiar can take my mind off the situation that I am in that I am not very good at dealing with. I hope that helps explain why people like keeping to the same. They are under stress.
The easiest way to get someone to explore new avenues are when they are not stressed, to take something they are familiar with like a hobby or past time that can be expanded upon. For example, if he likes castles, go and visit one. If he likes trains, go and see something train connected. While doing this one is giving oneself a change of enviroment with the journey. This is a good starting point... But it is much better to do it on his good days. Dont do it when he is stressed.