LOL
I'm really looking forward to know what is going on in the last chapters, after they did it. I think Jinwoo is starting to like Sangtae, since he initiate the kiss in the last chapter (and it was hot, admittedly).
Here are the raw chapters , it's not in his desk drawer, but just a drawer in his room. Guessing maybe it was his girlfriends and he is using it without her permission, as to say you want to break up over such a sight seems a bit much. Maybe it was the straw that broke the camels back and she can't deal with his new more agitated behaviour though?
https://toonkor.co/%EC%A0%95%EC%88%99%ED%95%9C_%EB%82%A8%EC%9E%90_14%ED%99%94.html
https://toonkor.co/%EC%A0%95%EC%88%99%ED%95%9C_%EB%82%A8%EC%9E%90_15%ED%99%94.html
or lezhin https://www.lezhin.com/ko/comic/modest

SPOILER FOR NXT CH (only doing this bc ITS FUCKING FUNNY)
So he starts masturbating but it isn’t enough for him so he uses a dildo AND THEN HIS GIRLFRIEND CATCHES HIM HAHAHA it’s probably not that funny but I was dying lmao