Read manga: Nidome No Isekai Shounen Datta Kare Wa Toshiue Kishi Ni Nari Dekiai Shitekuru

manga
Summary:

"The boy I saved before becomes an older and a highly talented knight!"One day, Sara was transported to another world and saved a boy named Luke who was pursued and collapsed in the forest for some reason, and decided to live together with him. However, just as Luke was beginning to recover from his wounds, Sara was abruptly sent back to her own world. Three years later, Sarah returned to the other world again and reunited with a 25-year-old Luke, the finest ice magician in the country and a knight who earned baronetcy for his achievements! He used to be 10 years younger than her, but now he's two years older and a romantic interest."I'll reward you with my entire life," he said as he began to dote on Sara.