The couple, in their early 20s, rented a room at the guest house through online booking and checked in yesterday, he said.
The woman's health condition deteriorated this afternoon when she started bleeding, following which her boyfriend took her to a nearby private hospital.
The hospital, however, refused admission. He then took her to a state-run medical establishment, where she was declared "brought dead", the officer said.
Police lodged a suo motu case and arrested the man as her death was due to "unknown reasons", and in his presence, the officer said.