Responses
I don't know if it's only me but I think he wanted to break up because he was pissed off with Taekyung's words when they were talking in the torture room about people dying, all of that. It's my opinion though, plus he already kept all of his anger towards Taekyung before. Maybe he just exploded.
I'm at chapter 20 but I can't understand why Siyeon wants to break up ??? Like you failed your job for which you engaged yourself, so of course Taekyung was angry at you, boyfriend or not ! He had every right to be angry