And this is why you need to solve your traumas before starting a relationship. Taseo had everything to be happy with Chunwoo but decided to live with guilt and shame about something that wasn't his matter. It was his parents. 
Please, if you are feeling something similar, be aware that the decisions that our parents make regarding their relationship are their matter, not yours. 
I'll love this story forever. I can't tell how many times I've read it.