
When i was like 14 i asked in a discord server if someone could trauma dump in my dms so i could use it as inspiration for my stories and literally no one got mad and multiple people dmed me and personally i think that's worse than what's going on in this story.
Most people don't care at all if you use them as inspiration for stories because that's literally how all stories are written they are a direct reflection of the author and their life experience and people they met throughout their life.
I don't understand why it's such a big deal in this story.

It's not that simple at all. There is actual reason. Juheon felt betrayed because all his life he was being used by other people because they get something in return by using him. It was explained how Juheon viewed Dohu as the only person ever to see him for himself, not for something he can be used for. It was obvious that Juheon would have forgiven Dohu if Dohu apologized, but we all know Dohu is slow when it comes to emotions, he is slow in making a decision. He was thinking if he should apologize for that, that he can just hide what his true intentions at the start first. That's where the drama started. Juheon was hurt because he felt used like he was before by other people and by Dohu of all people who he thought saw him for who he was, not for something else. And Dohu was slow to realize what he should have done or say to Juheon first. It isn't stupid. The reason for the drama is valid. It's not stupid at all. Just try to visualize yourself in their shoes.

3 things to consider,
1. You said "Most people don't care" so you yourself know that not everyone reacts to the trauma same way. And we should not expect all of them to have same reaction.
2. All those people who dm you knew that they are going to be an inspiration cause you asked for consent first, knowingly or unknowingly. Which was not something that dohu did before using juheon as an inspiration.
3. juheon's trauma is literally related to people using him. So its valid that he would get mad that someone he trusted had became close to him with ulterior motives. It does not matter if dohu's feelings changed later or not.
Not saying juheon is 100% innocent but let's not invalid his trauma just because we think that it not that serious if it happened to us just to defend dohu.

But the only thing mc was taking inspiration from juheon is his personality it wasn't his trauma or anything that would cause such a big argument, i could understand being like "wtf" at first but even with the trauma of being used i don't think being used as inspo for a fictional character by a friend/lover is something that can cause such a big reaction but oh well
The drama here is so stretchout. In any normal human interaction if someone said "I used you as an inspiration for my character" the person will be interesting or wont give a shit.
Author should've give ACTUAL reason for character feel betrayed. Like MC editor will push/persuade Dohu into relationship by saying this experience can help you with your book and levitate your career. Dohu would also at the start will say to his editor or friend that hes only doing it for book to confirm that this is fake relationship.
And after they started dating and Dohu genuinely fall in love, Juheon will find out that Dohu started this not because he likes him but because of his career (either editor will slip this info accidentally or Dohu friend slipped that its funny how this relationship started as fake). This will lead to confrontation and Dohu will admit that yeah IT WAS true which will lead to the current situation while also making drama REASONABLE.
THE REASON IS RIGHT HERE, AUTHOR.