Police said Wisut Sahasamut, 25, later called for an ambulance to help Noppadol Iamserm, 24.
Mr Wisut was waiting by the man's body when police arrived.
Pol Lt Phuriphat Phumek, a case officer at Klong Ha police station, said Mr Wisut has returned home after finishing a job painting at an ocean oil rig. He thought he would surprise his wife, but when he phoned her as he approached their home he got the feeling she was with someone else.
On arriving he found Noppadol, a former boyfriend of his wife, in the house.
The two men fought and Noppadol was beaten to the ground. Mr Wisut then called for emergency help but the rescue team said Noppadol was already dead when they arrived.
Mr Wisut confessed to hitting Noppadol and police charged him with assault causing death.