It's rare to find a manga like this to be honest. It stumbles upon very difficult subjects and complicated emotions and honestly, does this remarkably good.
The characters feel so real, their actions and emotions feel very genuine. I honestly cannot explain properly how close to home does it hits. I think anyone who has some past issues, depression, etc and has a hard time to overcome it and decided that it's better to pretend a fake smile not to get more hurt would understand Taehyun's behaviour. The fact that he would have a hard time believing in other people's feelings and wanting to test them out also feels very real.
On the other hand, Dayeol behavior is also easy to understand for someone, who is serious and is having a hard time dealing with multiple things in their life at once, when they have just one goal and no passion towards it. He overanalyzes things but also gets his feelings involved easily. I react to his story on an emotional level and I think all his actions are so real. I would act exactly this same, feeling pissed at Taehyun for his actions but at the same time stuck thinking about him, because I don't understand him and wanting to know why does he act like this and being totally swept away by hearing his story. I honestly love this, the emotional struggle, their actions - everything seems so genuine. You can feel the author has a very good understanding of human emotions and is very good at reproducing them in her work. And you have to admit, the art is simply marvelous.
The only thing before you read, this is more of a shounen-ai than yaoi to be honest, which I think fits the story very well. They are both just exploring and are already in late high-school/college, so no wonder they take their time.

I really loved this!! I think it's worth a re-read one day.