let me see if i understand

the bottle of water is driving me crazy i think he's using it as some sort of a timer like a sand hourglass ┑(￣Д ￣)┍

There are some pills in the water if I remember correctly...

Hhm nah sorry I was wrong. But it rlly looks like he uses it as a kind of hourglass

It is a water clock, the predecessor of the sand hourglass. It is a measurement of time so he knows how long his captor stays away. He isn't aiming for an accurate hour, just consistency. Also, having a measurement of time might help him keep his sanity, because when he was losing track of time while chained to the bed, he lost track of reality as well. My only problem with his timepiece is that he didn't use a piece of tape from the med kit to seal the pinhole in the carton. It should have leaked in the fridge. Good MacGyver gadget otherwise.

That diary has me all kinds of confused. Nothing in the wording suggests they were anything but friends. Nothing in Dohyun's memories shows evidence to back up an intimate relationship either. Poking someone and tickling are too innocent to suggest Dohyun locked Sungho in a gym room, starved him, and raped him, or had a sexual relationship. Also, the time frame is pretty short to go from playful teasing and video games to a sexual relationship. The surgery had nothing to do with his head injury. Dohyun made an educated guess that his captor is raping him to recreate the past, and Sungho has accused him of leaving him starving and wasting away. But there is too much conjecture and baseless assumptions in the explanation the author has given us so far. I really think something else is going on, but Dohyun has to remember the whole of it. What I have pieced together is Sungho was a loner that no one noticed was absent during his surgery and hospital stay. Dohyun initiated their friendship on a whim. Sungho probably had a crush and overestimated their intimacy, and felt betrayed when Dohyun faded him out. While Dohyun could be accused of being insensitive and flaky, I find it hard to believe he committed physical/sexual assault. I think the "starving" was metaphorical, the starving of an unrequited love that had access to his crush, and was then neglected. While I agree Sungho is raping on a schedule correlating to the blank dates in the old diary, I don't know the significance of those dates or the ending message or crying memory. Sungho's head injury and lack of expression make me think he's got some serious damage (unrelated to his surgery), and the new rape diary shows some gross disconnect between his thoughts, actions, and understanding of body language. I think he's a fixer by trade, and that his damage makes it easy for him. I also think his boss/client has sent someone to tail him because the old man doesn't like the unexplained absences and strange behavior. Maybe Dohyun will be discovered.

Thanks so much for the explanation! I also doubt Dohyun sexually assaulted Sungho when younger. I have the theory that they fooled around but Sungho was the only one with the crush (or the only one willing to show it, with Dohyun potentially scared of being homosexual), and ultimately felt betrayed. But, as you said, there's no evidence yet of an intimate relationship yet. I agree with everything else, and I'm glad you mention Sungho's boss, since he made some moves but not more has been shown, it could be that they discover Dohyun.