
i still cant get mad at Jihwa so idk why yall are mad at him to the point that u want him to die (-.-) anyway i couldnt figured out his illness... like what it is? im curious...

The "illness" the father is taking about is homosexuality. The way he describes it ("wayward yang energy") is how homophobic people used to talk about homosexuality a long time ago. Words such as homosexual, gay etc. didn't exist until a century ago or something. There are still languages today that don't have a word for homosexuality.
Obviously, being gay per se is not a mental illness. However, the discrimination that LGBT+ people experience causes mental health issues. SH was traumatised by his father by being isolated, beaten and who knows what else happened to him. Hence SH suffers from depression, insomnia, anxiety (?) etc. today and needs medicine or drugs to calm down or escape from reality/his feelings.

What do you mean? If we were in Jihwa's shoes we would do the same and try to kill someone?? Uhm, no. We wouldn't.
Sure we would be sad etc but eventually people move on, once they see their beloved ignoring and hurting them. I have only met one person, who had a hard time moving on, because a friend of theirs tried to end their friendship, and that person was borderline.
You just got bitten by a super duper big mosquito. You should be careful next time uh- the mosquito also has big di— no nevermind.