
Tell him so that he could pity him?
I dont think he deserve to know about his illness.... the person who lost his family carrier dreams everything for him and he was cheating for 3years has he ever told him about that? left him alone to be with his another lover , calling his some one else's name while sleeping with him.... this kind of scum doesn't deserve an explanation.
10yrs worth of feelings isnt easy too erase .... he cant forget the love with him nor can he hate him totally ....so he decided to leave ....

Spoiler IG
Its revealed in the novel that the uke does nothing about the cheating seme beacuse prior to them getting "married" , the ukes parents found out about them and didn't agree to their relationship.The uke upset, eloped with the seme without his parents consent and shortly after his parents got in an accident and died (I think car crash can't remember).After the uke gets informed of his parents passing he gets depressed and he ends up blaming himself for their death .His mentality towards the seme's actions and cheating were him thinking that its his attonment for leaving everything behind for the pursue and "love" of the seme.My I add that the seme was always selfish,in the novel it states that he never loved the uke as much as himself he's extremely egotistical and only truly saw things for what they were when he was informed of the ukes illness and death always taking his love for granted,until it was to late.But I can see why you blame both sides,given their relationship in which they had no communication.And it was suggested that the same committed suicide a few years later.Hoped this helped view his situation more clearly.
I’ve never had this kinda situation where I don’t know who to hate and who to pity, everybody’s to blame. Now that He Zhishus going all out to guilt trip this guy, why in the WORLD wouldn’t he tell him about cancer, leave him and get the fuck together with the doctor?!?!