Even if Cheongsun had found the letter 10 years ago, the most they could’ve had was a short long distance relationship. 10 years ago, Cheongsun was very insecure about his class and family status, it’s the reason he broke up with his first girlfriend. He saw Gonghyun as living in a completely different world than him and eventually it would’ve eaten away at their relationship at that young age, especially with the stressors of school and finding a job. They both needed the 10 years to become more financially independent and self-assured. The reason journal was only shown at the ending is because it doesn’t matter that much in the plot, it doesn’t change things. Now that they’re finally together, they have the rest of their lives to tell each other secrets and feelings they couldn’t have expressed when they were younger.
I’m betting that they met before and ML used to be a plain-looking nerd that the MC was nice to/said something encouraging to and ML became obsessed so he changed himself to be the MC’s ideal man.
Even if Cheongsun had found the letter 10 years ago, the most they could’ve had was a short long distance relationship. 10 years ago, Cheongsun was very insecure about his class and family status, it’s the reason he broke up with his first girlfriend. He saw Gonghyun as living in a completely different world than him and eventually it would’ve eaten away at their relationship at that young age, especially with the stressors of school and finding a job. They both needed the 10 years to become more financially independent and self-assured. The reason journal was only shown at the ending is because it doesn’t matter that much in the plot, it doesn’t change things. Now that they’re finally together, they have the rest of their lives to tell each other secrets and feelings they couldn’t have expressed when they were younger.