I think he caused it and told the dudes to do that to him
yikes
To my understanding, Hyunwoo really likes Jisoo. But he was dying because of his mystery illness and at some point he'll have to leave Jisoo.
But Jisoo was always being bullied by Sungbum when he's not around, so he need something to make the bullies leave Jisoo alone.
I think that's why he had planned that assault on Jisoo, to record Sungbum in the act. So that the video footage would be of a great help for Jisoo to blackmail Sungbum.
He was trying to help, but because he doesn't have the time, he did it in the wrong way.
Jisoo's suicide attempt was just not something that he expected, I guess.
I'm like 2 years late but he was the reason why Jisoo was getting bullied. He liked Jisoo in a fucked up way and wanted to hurt him because he was also jealous of him in an odd sense. He gave the phone as a "gift" after being the one who orchestrated the whole rape attempt on Jisoo, because he wanted to return the favour of Jisoo painting him his picture.
None of it was ever for Jisoo's well being or out of the goodness of his heart.
Wait what did hyunwoo do? wasnt he taking care of jisoo? didnt he like him? He did come to o save jisoo while he was being attacked right?