Complex sentence: He was able to win Jia Di's heart but unfortunately he soon discover that he has Wilson's Disease and he was reluctant to tell it to her since he doesn't want her to be lonely when he dies.
Split into simpler sentences: He was able to win Jia Di's heart but unfortunately he soon discovers that he has Wilson's Disease. He is reluctant to tell Jia Di since he doesn't want her to be lonely when he dies.