does anyone understand what is the milk play? when dohyun collected something from the mil...

I think the milk was already expired, and he's mixing the water and the spoiled milk to maybe poison the Seme, but I think the author forgot about it ε=ε=(ノ≧∇≦)ノ

the milk play is when sungho forced milk into dohyun’s mouth and told him not to swallow it as he blew him (think of it as a mild torture play)

I think the milk carton into the water bottle was to keep track of when the Seme was arriving, such as finishing his work which was usually about two water bottle dents, he did it at the beginning to see when he arrived, and later did it again so he could read the diary and know when he was close to coming back since there was no clock.