I wouldn't call the brother delusional if anything I feel sorry for him. Firstly, he feels feelings for someone he initially shouldn't feel for- a brother. From the last few chapters, we can see Sunwoo feels guilt and we don't know if he will get over that guilt and try to fight for Jungyeon. Secondly, the fact that there is a boyfriend will probably make him feel guilty if he does do anything. Sunwoo is definitely not the type to be aggressive especially in love even Jungyeon and his classmates see him as a soft bunny; a person such as this can never be aggressive but can be loving and affectionate making their relationships last long. Lastly, if he does choose to not fight for Jungyeon he will be forced to feel unrequited love and watch as the person he loves be swindled away. That in itself makes him the most pitiful character from what I can see/read so far in this manhwa.
I will choose the couple the mysterious boyfriend and Blondie..
cuz I feel it..