To be fair, Seungho did give Nakyum a chance to explain and tried to talk to him. Actually...

To be fair, Seungho did give Nakyum a chance to explain and tried to talk to him. Actually I was amazed at his self control, waiting patiently for Nakyum to wake up. Unfortunately Nakyum was too afraid to talk, which is understandable, Nameless threatened him and he was probably still in shock after such a traumatic experience.
We always complain about their lack of comunicación but Seungho did express his feelings to Nakyum several times. In this chapter he's confessing to Nakyum again how he feels about him. Now it was Nakyum's turn to communicate. Seungho's frustration is understandable, he's desperately trying to get some answers but all he gets is "I'm sorry my lord". All the evidence points to Nakyum running away. How is he supposed to know that he was kidnapped and then returned? 
He thought that Nakyum's loving embrace and heartbeat meant that his feelings were reciprocated but now this happens, his insecurities came back and he feels betrayed. It's sad that due to his mental health problems turning to violence is second nature to him. 
Of course none of this is Nakyum's fault. That's why it's so sad, they're both suffering and don't know how to deal with their feelings. 
I would hate to see Seungho force himself on Nakyum again. I hope he notices marks on Nakyum's wrists or something like that to make him stop.