Of Human Bondage by William Somerset Maugham

Philip was restless and dissatisfied. Hayward's poetic allusions troubled his imagination, and his soul yearned for romance. At least that was how he put it to himself.

And it happened that an incident was taking place in Frau Erlin's house which increased Philip's preoccupation with the matter of sex. Two or three times on his walks among the hills he had met Fräulein Cäcilie wandering by herself. He had passed her with a bow, and a few yards further on had seen the Chinaman. He thought nothing of it; but one evening on his way home, when night had already fallen, he passed two people walking very close together. Hearing his footstep, they separated quickly, and though he could not see well in the darkness he was almost certain they were Cäcilie and Herr Sung. Their rapid movement apart suggested that they had been walking arm in arm. Philip was puzzled and surprised. He had never paid much attention to Fräulein Cäcilie. She was a plain girl, with a square face and blunt features. She could not have been more than sixteen, since she still wore her long fair hair in a plait.