
Joowon isn't gay lol if anything he's bi or "Heesoo-sexual". I'm pretty sure that one of the translators on ig said that the author gave an answer in the Q&A that Joowon is having or had(?) a lot of girlfriends on the side and if anything i think it was hinted pretty clearly in the chapter in which Heesoo got nervous and started scratching his nail while watching that interview about Joowon talking about his future, marriage and children.

Sexuality isn’t something that just suddenly changes. Why do you not want him to be gay?
I’m against his sexuality being a choice that can be changed, swapped or anything like that.
As said prior, I don’t think it’s right for who is attracted to change to fit any agenda or where there are token gay/straight couples or characters. I don’t care if he is bisexual, but it will be wrong to make him go with a girl just for that. Or for him to go a character rarely mentioned at all just to pair him off and not to be paid attention to. I want characters not fillers.

Do you not think they mentioned it because it is a common cliche that men can’t go out with men because it would ruin their lives and they need to marry a woman and have children? It’s literally in plenty of yaoi. Some guy runs away because him being gay would ruin him. Even if Joowon wants children and marriage he could get it in the right places and adopt so he could have it if he wanted it with a man. It’s just not socially acceptable and of course the parents thing. But yes he could be bisexual and that would be fine, never said he had to be gay and all that. But I don’t want him dating a girl because they need some token straight couple or gay couple. Gay people can have a gay community around them. And as said, she was literally some filler character he planned on using to make Joowon jealous. I would be for it if she was a character actually. I am not against him being bisexual, but a whole “I just needed you to reject me and now I’m straight” type of thing is a no. You don’t develop feelings and fuck dudes and call yourself straight. Sexuality isn’t rejection based but something you can’t help. But oh well.

Nobody is trying to change his sexuality or saying that sexual orientation is a choice. Like at this point you're just trying to convince yourself what Jowoons character is supposedly like, which obviously doesn't match up with the way that he is written.
And about Jowoon ending up with a female.. i mean she doesn't seem like a filler to me:
https://toonkor.dog/%EB%9F%AC%EB%B8%8C_%EC%98%A4%EC%96%B4_%ED%97%A4%EC%9D%B4%ED%8A%B8_39%ED%99%94.html
┑( ̄Д  ̄)┍
Soooo nobody cares about Joowon?
I hope Joowon gets someone who loves him. He seems to really have feelings for MC but he will always be rejected really. Haesoo helped create what he doesn’t really like and Joowon plays along for him. It’s old now. The things they play. I hope Joowon can get someone for him. You’re alright Haesoo, but if you’re not ending up with my baby please be gentle with him. My heart hurts knowing Haesoo has this whole other blossoming love while Joowon will most likely just be dumped. Drug along. The saddest part about love triangles is the broken hearts.