I'm feeling unsure about getting married and it might be too late to tell my fiance.
Do you think it's good to tell him about this and what are you doubtful about?
I haven't made my decision yet.
If you are questioning whether or not to get married then you should not go through with it. You should feel confident that this is the person you want to be with forever before you get married.
I want to make a commitment, but I could change my opinion anytime.
Your uncertainty is telling and if you don't want to be with your fiance forever then it's best for both of you that you not get married. Going into marriage with such doubts is likely to not end well.