Sorry for the refusal of the student visa of your fiance. Unfortunately, if your fiance doesn't change his situation and tries again, there is a high chance his visa would be rejected again.
The immigration officer doesn't deny a student visa based on his or her personal reasons. There are rules and guidelines that the immigration officer uses to make sure students are really eligible to study in Germany. Your fiance was denied because he didn't meet one or most of those rules.
I would advise your fiance to carefully look at the reasons given by the immigration officer and work on them before appearing for an interview again in the next semester.