
That's right. He's soft, the kind of character that people would call 'boring' because he only pursue the man he likes and that's all. But I think he's cute. Or, at least, if I have to prefer between him and the professor I choose Eun woo.
I bet that, if he was the protagonist and readers would have started the manwha with his point of view, most of them would have hated the professor. Let's think to ukes like the uke from BJ Alex or Yours to claim. In what they are different from Eun woo? We just start the reading from their pov so we feel closer to them.

Yepp true, like if we see in eunwoo's pov, prof will be the all and all love rival we all hate the most that want to steal the seme, but then again rn we're seeing prof in hajoon's pov, so he looks like a hot second love interest instead... Eunwoo kinda got pushed away from the story too rn my poor bebe :'(

Aww that's what I thought too! And I would really hate if author would only use Eun woo to get Hajoon and Prof together. I mean poor Eun woo! Not only he was messed around by the professor he loved so much but author makes also him develope feelings for Hajoon. If Hajoon ends up with Prof that would be double hurting for Eunwoo: the two persons he fell in love, both leaving him and getting into a relationship.
I mean... Ok, probably that would be different from other mangas and manwhas but... That would be ways too cruel to Eum woo.

You should know that being a jerk can't be defined 'personality'. If we talk about a stronger character, then I'd give you a point. But here we simply have someone who have fun messing with people and not caring at all about their feelings. He only does what he wants and doesn't care if other characters are hurt in the process. If you like these kind of charas why don't you read 'Nurenezumitachi No Koi'? It's really similar. If you like the prof in this story, probably you will like the sensei in that story.
But look, I bet there are high chances you won't like him. Know why? Spoiler: Because he hurts the seme. And this is what I can't stand.
What I really can't stand is that now that was Eun woo to be hurt, you won't care... but if prof will jurt Hajoon in the future probably a lot of people and you will probably dislike him.
Plus, you are right: this is a story and not real. I have to bear with too many jerks in reality. I can't stand to see them in stories too.
It makes me laugh how people keeps saying that they don't like Eun woo because "he's a slut" or because he's not interesting.
So... About him being a slut. In what exactly is he different from professor? The only difference is that he is a bottom and prof is a switch. That's all, literally. Plus Eun woo doesn't fuck with whoever but it was only with professor. He started doing it with Hajoon only because professor said it. Later he took a liking on it because he started developing feelings for him. So the real slut is only the professor.
Secondly, about him being ordinary... We literally know NOTHING, not about Eun woo, not about professor. We only know that Eun woo liked professor and that professor likes fooling around and mess with people. If interesting means having a twisted personality and step on people's feelings (like the professor do with Eun woo, knowing he likes him seriously but messing around with him anyway)... Then I give up on trying do understand your point of view, seriously.
To me he's not interesting. He's only a total jerk. He's not different from the sensei in "Nurenezumitachi No Koi". Probably they're not cliché but I prefer plain characters to jerks.