The man, identified as Gurusamy, a mill worker and father of two children, was having a love affair with the 20-year-old woman, they said.
They had an argument while travelling in a bus from Rajapalayam to Srivilliputhur following which the conductor asked them to get off as the other passengers were getting disturbed, police said.
In a fit of rage, Gurusamy attacked her with a sickle, they said.
Fearing that the woman has died, Gurusamy allegedly hanged himself from a tree near the spot, police said, adding, the woman has been admitted to a hospital in a serious condition.