An Engagement Ring Out of the Blue - My CEO's Love Is Just Too Much

“Didn’t we get engaged just last night?” When office worker Hiroko, a serious 32‑year‑old whose only charm is her earnestness, wakes up from the worst night of her life, she finds the “scary‑faced prince” from a client company lying naked beside her. Every day she endures sexual harassment from her boss and unreasonable behavior from her junior coworker, clinging to the hope that she’ll soon marry her boyfriend from college. But just as she starts expecting a proposal, she discovers he’s been cheating on her. In rock‑bottom despair, she goes on a drinking binge—and the next morning, there’s an unfamiliar ring glittering on the ring finger of her left hand…!?
https://www.cmoa.jp/title/358513/