I felt so uncomfortable. Being on drug doesn't excuse anything I loved this webtoon before...

Yes and no.
He was drugged, almost heterosexually raped, then was manipulated to rape Jin.
Hardcore drugs put you under a trance-like state, even susceptible to brainwashing.
You become delusional and can't tell the difference between reality and fiction.

Now... continued use of a drug, while knowing it will fuck you up, or going into doing a drug that you know will fuck you up-- that's a choice and not excusable.

That's why I have no pity for chosen addictions.