When people tell you the way that you think is wrong or do something along the lines of abuse it can cause so many issues. Internalized homophobia is what I think went on and is still going on with him. Not to mention the fact that so far we have never seen a sign of Seungho having a close relationship with anyone from his family. He has never felt loved and now he can't distinguish it. That also probably why he never noticed Jihwa's feelings.
True. I can see where he is coming from but with Seungho he seems to be a literal person as well. Jihwa (from what we have seen) hasn't really confessed. He has just been there and expected something to happen. Like maybe he'll notice if I stay but that's just not it. Trust me I have been on both ends and feelings are confusing.
Ok so on the topic of the disease we all know that it was just him being gay but they did something to him for it. I think he developed some mental illness or rather now he just doesn't know how to distinguish emotions correctly and is going through a bunch of stuff mentally because of it. Almost as if all of those guys he hurt even though he sleeps with them is due to some internalized homophobia.