It's confusing to work out what actually happened between Sungho and Dohyun in high school so I wanted to share what I've worked out.
They meet in their first year of high school and are in the same class (this is important for working out when exactly the flashbacks are happening). They become friends and start hanging out spring and Dohyun develops feelings for Sungho in summer (ch 41). He kisses Sungho but Sungho rejects him.
They carry on being friends after this (ch 43, 45) and sometime before the end of the first year Sungho kisses Dohyun and says he doesn't feel the same but he can handle a kiss (ch 45). There's still no sex happening.
Then they move up to second year and get split into different classes. They can't hang out as much and Dohyun starts to distance himself believing it to be inevitable (ch 45). In March (the beginning of the school year) Sungho goes into hospital for appendicitis and Dohyun doesn't seem to notice he was gone. Sungho is unhappy about them not spending time together (ch 24, 45).
It's not until August 25th that Sungho has sex with Dohyun to stop them drifting apart. Dohyun realises how much Sungho cares about him and goes along with it because he thinks this will give Sungho a reason to stay with him (ch 46). They keep on having sex until November when the whole warehouse thing happens and they break up.
So basically the diary is only from the second year of high school, when Sungho had known Dohyun for a year. They were friends for more than a year and in a sexual relationship for only about 3 months. Dohyun didn't distance himself from Sungho because Sungho wouldn't have sex with him--they went back to being normal friends after Dohyun kissed him.
The authors had a twitter poll ages ago asking who people wanted as the top and bottom in the pairing.
It was really close but top!Joseph won (I voted that).
So now you know who to blame.
I want top Joseph too so thank you for voting
HOLY FRICKING GOD THANK YOU