Ranjana, 20, hanged herself from a ceiling fan at her boyfriend's house in Delhi's Naraina area Saturday.
Vikash Jain, the girl's boyfriend, found her dead around 6 p.m. when he returned from office.
"The girl's family members told us that she used to keep the keys of Vikash's house and had gone there to offer him food," a police official said.
"Ranjana fell in love with Vikash, who works with a private firm, few months ago. She had been asking him to marry her." Vikash, however, refused because he was already married.
"It might be the reason why she took the extreme step," the official said.
While Ranjana's autopsy report is awaited, Vikash is being questioned by police.