Is there a law against sexual harrassment applicable for the following situation

Girl and boy are friends and share good and bad times. Boy likes girl. Girl doesn't like the boy, clarifies the stand, but remains as friends. When the girl gets engaged eventually, boy doesn't take responsibility of his sad state of affairs and entirely puts the blame on the girl. Boy sends threatening mails and phone calls to the girl after she announces her engagement with really no case for himself. When can the threats be treated as mental harrassment by law? When should the police be called? The girl is only afraid that the boy may cause any disruption during the wedding or continue to mentally torture her before, during and after the wedding.