he was depressed because of Tingwan's car accident, and thought that it was his fault, therefore he broke their relationship, coz he was afraid that Tingwan would be unhappy with him. this is just what I read in the novel, after reading it, I can't blame Suyan at all. and this is just my opinion, don't be angry guys
the novel not translated, u can use translate option on browser https://czbooks.net/n/cpme7j5
I think there is a scene where he is jealous of uke, but it's not that big. coz the focus of the story is abt uke who tries to change so that he can be worthy of being together again, coz previously the uke didnt love seme at all. So, the next story will remain like this, close without a clear relationship status, and uke tries to make seme want to come back to him. But please don't blame seme, coz his mental health is actually weak due to events in the past, because his brother committed suicide, and secondly because his uke's accident.

Well... that completely shattered my heart , right after the break up you slept with another person? Now I see who’s the scumbag now (╬ ̄皿 ̄)凸 someone please tell me there is gonna be a happy ending my heart hurts ╥﹏╥