I saw the Raws, NOOOO, they don't have sex, there is harm but no sex. I understand the fear because most Manhwas take that course, and it's messed up. But one of the reasons we (or at least I) like this manhwa is because for all this time, it has been one of the few that respect (most) boundaries and it depict depression in a truthfull manner.
MORE SPOILERS
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SPARK NOTES:
Yoon cuts himself because he was worried for Taemin.
Basically, Yoon calls Taemin, and Taemin chose to not answer the phone. That call could have saved him, and in not answering, he showed how he wanted to die.
Yoon became...a lot of crazy over this and wanted to guilt trip him, so he cuts himself using Taemins hand, thinking that maybe Taemin would feel more guilt towards him and decided to live out of guilt.
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EVEN MORE SPOILERS
WELL FUDGE, I was wrong and shot myself in the foot for openingmy big mouth. It only ook like two more chapters, and the sex started ( https://tenor.com/b0vS8.gif)
Why am I even showing off about that? (Time between sex) If they break my own reality later (╯°Д °)╯╧╧
FOR THOSE THAT WANT TO READ THE SPOILERS IN (some grammatical errors) ENGLISH:
https://vymanga.org/manga/payback/chapter-90/