My Regressed Sister Covets My Fiancé

I got engaged on behalf of my sister. It was a command from our father, who always favored only my sister. After a week of travel, I finally arrived at the Duke’s castle. “Oh, you’re here now? Nereis.” My sister, who had arrived earlier, greeted me. “I’ve changed my mind. So, you should give it up.” Suddenly, my sister, who now coveted the position of the Duke’s wife, and “I like you, though.” The Duke, who kept approaching me regardless. The incomprehensible situation didn’t end there. Upon accidentally discovering my sister’s diary, it seems she has somehow returned to the past. And this time-traveled sister of mine, she covets my fiancé.