The term unlucky stars means to have bad luck in your life. In the prologue it has the line “A pair of star cross’d lovers take their life.” This line says that Romeo and Juliet are unlucky lovers. The line also says that they will take their own lives. Maybe this line could be saying by unlucky and odd circumstances these two lovers will take their own lives.
How does this connect to Romeo and Juliet? Romeo and Juliet have a lot of unlucky things happen to them.