I Realized My Fiancé Is the Protagonist of an Eroge, so I Want to Break Off the Engagement

Elizabeth Miller, a 16-year-old count's daughter, attends the Royal Academy. One day, the shock of witnessing her fiancé Gilbert cheating on her triggers memories of her past life. She realizes that this world is a male-targeted "ero game" she once played, and Gilbert is the game's protagonist—a scumbag who cheats on his fiancée with multiple women across the academy. Determined to break off the engagement, Elizabeth sets out to reclaim her future.
https://www.cmoa.jp/title/351164