You need:
Picture of both parties together or write the names on a piece of paper
A burning dish
Cut the paper between the two of you and say:
As I cut their tie let the bond between them be broken.
Burn both halves of the paper apart. Say:
As I burn the tie let the bond be ever severed. So Mote it be!
Thank the deities and dismiss the circle if you have used one.
Bury or scatter the ashes.