My fiancee, who has just been engaged for a month, wants to break up because I can't give her a definite wedding time. My mother wants to wait until my sister is engaged.

I think your fiancee may be insecure about your relationship. . After all, people who love each other are engaged for a month, and they will not wait until the end of the year! Otherwise there are other reasons. I have always really felt that love can face all problems. Coax him more and show your determination.