
I don’t think Jay did it because of anger. Jay did that at chapter 89 for a reason, MC is very mentally unstable, he has no reason to live after the revenge was done. There is no stopping the MC trying to end his own life 2nd time or 3rd time. And next time they all won’t be so lucky and save MC in time. What Jay did at chapter 89, was Jay telling MC when MC not picking up the phone call trying to give up on his life, MC didn’t just kill himself, MC also kill Jay in the process too, because MC was loved and wanted. Jay wanted that scene at Chapter 89 to scarve into MC mind so if next time MC wanted to give up living again in hope that this scene will stop MC from trying.

Holy Cannoli, I did not realize how many people would want to know!
~The following message contains spoilers. Readers be advised. ~
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Jay visits Yoohan at night, in the hospital. While Yoohan is asleep, he looms over him in silence. Feeling someone's presence, Yoohan wakes to find Jay staring at him, but his eyes are cold. Jay sits down on the hospital bed, and strokes Yoohan's cheek tenderly before turning away from Yoohan, not able to look at him. After a protracted silence, Yoohan asks, "Are you mad?"
"Yes." Jay pauses, before continuing, "I've watched the video... the movie scene where you commit suicide."
"What was wrong with it? Why are you so annoyed?" Yoohan asks, not understanding.
Jay explains how after watching that scene, he immediately called Yoohan, but couldn't get through, because Yoohan was on the phone with someone else for nearly 20 minutes. He thought that strange, as Yoohan promised to be right over. Unsettled, he tracked Yoohan's location and rushed over, but when he got there...
The memory of finding Yoohan bleeding to death on the street replayed in his mind.
It was then, he knew.
Looking at the carnage before him, he instinctively knew Yoohan ignored his call. The blood on his cellphone all but confirmed it...
"Were you unable to get my call... or did you ignore it?" Jay asked flatly, his back to Yoohan.
Yoohan struggled to answer.
"Here's what I thought... about your suicide scene." Jay starts, as he pulls out the knife Yoohan had bought from the street vendor... the knife that almost claimed Yoohan's life.
"Unless there's a force... a reason... that has more influence and power over you than I do... than no matter what... when faced with the ultimatum between me or death... you'll always choose death." He positions the black handle towards Yoohan.
Yoohan gasps, startled, as he recognizes the knife even in the dark hospital room.
"Answer me." Jay demands, as he touches his forehead to Yoohan's. "Was it that you couldn't answer my call... or that you ignored it?" Jay grabs Yoohan's hands and wraps them around the knife's handle, and holds them in place... with the edge of the blade facing Jay.
"I..." Yoohan's voice breaks, as he trembles at the sight of the weapon that almost claimed his life. The weapon Jay is now forcing him to hold.
Jay's gaze darkens.
Yoohan starts to hyperventilate.
"Was it because of your guilt toward your family's death?" Jay pressed, prodding the emotional wound that has caused such devastating, physical harm.
"Let me go!!!" Yoohan breaths heavily as his heart pounds. His eyes are locked on the knife as the memory of bleeding to death flashes in his mind.
"Pay attention." A menacing grin spreads across Jay's face.
"NO!! WAIT! WAIT---"
Still clenching Yoohan's hands around the knife's handle, Jay thrusts the blade into his wrist. Blood splatters and trickles down his arm.
Yoohan, in shock, looks on horrified.
"Now... I'll make you feel guilty towards me." Jay seizes Yoohan's wrist and pulls it towards him. Clutching firmly, Jay presses his open wound over the top of Yoohan's hand, letting his blood spill over him.
"Lee Yoohan... How does it feel to kill me?" With perverse satisfaction, Jay smiles.

I understand what Jay was trying to do and what result he was trying to achieve... I just don't agree with his methods. He's traumatizing Yoohan further...because God forbid we choose a healthy mode of recovery/healing. (Thus is life in fiction, I guess... ) I also know this is a turning point for Jay's character... as he becomes more controlling of Yoohan... and again, I just wish there were better ways to address the shared trauma.
Anyway!! I do appreciate you taking the time to respond! I agree with your explanation of Jay's intentions/mental machinations lol

Yes, sorry! I didn't see your reply!
~The following message contains spoilers, readers be advised~
While Taemin is in the hospital, his road manager comes to visit him. He opens a laptop that plays live footage of the board meeting Jay is attending.
There's a whole 1.5 chapters dedicated to the back and forth discussions regarding Dream Planning and Dream Entertainment, which is being viewed by Taemin. So I will summerize lol
The largest shareholder of Dream Entertainment is H Corp, and the chairman of H Corp is Chairman Han. Now Chairman Han, the CEO of Dream Entertainment, CEO Jung, and executive director Jay Yoon are all on one side.
Chairman Kim and his people are on the opposing side, and are in charge of Dream Planning.
Executive Director Yoon acquired the public performance license/copyright for the song that's critical to the plot of the movie, The Memory, which Dream Planning is currently in charge of. Director Yoon states quite dryly that he has no intention of letting Chairman Kim use the song, and that without it, they cannot move forward with the movie because it would be a breach of contract with the author.
If there is a breach of contract for the movie (with the author) due to negligence from Dream Planning, then Dream Entertainment holds the right to terminate their contract with Dream Planning for producing the movie. Since Dream Planning is unable to produce the movie, they are unable to fulfill the terms of their contract with Dream Entertainment, and Dream Entertainment will sue for damages (e.g. costs incurred for advertising, salaries, etc.)
It is revealed that Chairman Han gave all his shares of Dream Entertainment to Director Yoon, which makes the majority holder of Dream Entertainment... Jay Yoon... who is now the effective owner of Dream Entertainment.
Since Director Yoon already gave all his shares of Dream Planning to Chairman Kim, he will not suffer further financial losses from the oncoming lawsuit against Dream Planning.
Now in charge of Dream Entertainment, Director Yoon can now make the movie, The Memory, himself... and we all know who he wants cast in it lol
After the board meeting concludes, and we see Chairman Kim and Director Yoon in a heated argument (Chairman Kim is yelling at Jay while Jay is calmly menacing), the road manager leaves and tells Taemin to rest.
A couple of visitors stop by to talk with Taemin. Then finally, Jay visits Taemin again. Jay falls asleep on the hospital bed while holding Taemin... but when Jay wakes up... he's back to being his sadistic self T_T
Every time I read this chapter, I get more upset with Jay for what he does in chapter 89. I know he's upset at Yoohan/Taemin because he purposefully didn't answer his call, giving in to death, but venting your anger by traumatizing Yoohan more isn't the answer T_T He's been through enough -_-