Tbh even IF Guwon didn't kill his father, which we will see at some point, it wouldn't change the fact that Guwon is a bad guy. He killed people, he will continue killing people. He uses and plays with them like livestock. Of course killing the MC's father would deal even greater damage but even if he wouldn't have done it, Guwon still did things that go against Teach's morals and he would still be against it.
I have the feeling that Guwon is gonna turn into some sort of a yandere, I can practically smell it in the air. Thoughts and prayers to poor Jinwoo