Complex sentence: He becomes attracted to Alan's fiancee Madge, the prettiest girl in town, and is likewise adored by Millie, Madge's younger sister and Rosemary, a teacher who rents a room from their mother.
Split into simpler sentences: He becomes attracted to Alan's fiancee Madge, the prettiest girl in town, while he is likewise adored by Millie, Madge's younger sister. He also catches the eye of Rosemary, a teacher who rents a room from their mother.