He wasn't deaf

Xi Yuan still remembered the day Elena had died. He was in coincidentally City M then. He had never seen Sun Cheng so distressed, so helpless before. He wasn't stable. Neither emotionally, nor mentally. Elena and he had a love marriage three years after they had met in Chicago. The two were crazy for each other. So when the girl left him, Sun Cheng was beyond traumatized. He wasn't in any state to deal with the hospital paperwork or the death rituals. 

At that time, Xi Yuan had managed Elena's cremation, and her medical reports, and the hospital finances. All by himself. Sun Cheng had been a close friend to him, after all. It was then that he had found out about Elena's pregnancy. He couldn't imagine how his friend would've digested the news then. 'It is better for him to not know', he had figured. Since then, he had kept the secret caged inside his heart.