Ahhh now it makes a lot of sense about those nightmares they are probably about things that happened in the past. Sunbae might've been a sadist and done those things to him and now that he's with the baker he's obviously scared of the same thing happening even if he hasn't realized it yet his body has the trauma from the past.
I feel so sad for Sun Hwa everything keeps reminding him of his past and all goes back to the shit his ex aka Sunbae did he destroyed Sun Hwa's life with betrayal and painful memories even to the point where he would destroy others life and make it seem like it was Sun Hwa that did it always make it seem that it was him at fault and he would break down and run from it. i hope Sun Hwa will overcome it and get a happy life in the future without hurting and running from his problems and try to fix the misunderstandings