Superintendent Pedro Ubaldo, Bauang police chief, said the victim, Peter Lionel Smither, 57, of New South Wales, Australia, died in a hospital in San Fernando City due to four gunshot wounds, including one in the head.
Smithers live-in partner, Analyn Tabtaumabcao, 24, a native of Luna, La Union, is now in the custody of the Bauang police.
Tabtaumabcao tried to shoot herself with the caliber .38 revolver she had used in killing Smither, but the gun malfunctioned, Ubaldo said.
When the gun failed to fire, she tried to drown herself 50 meters away from the shoreline, but members of the Bauang Baywatch team saved and rushed her to the Ilocos Training Regional Medical Center.
Police said the couple had been living together at the Corpuz Apartments in Barangay Paringao here for eight months.
But authorities said they had always been quarreling over money problems and lately, over Smithers alleged affair with another woman.
Ubaldo said they have informed the Australian Embassy about Smithers death.