@jani sorry to break it to u, but unfortunately it's not an existing Manhwa.. It's a fan made of byul on how he will look like when he grow up ( There's no Love is an Illusion! Superstar yet)

@rojina Same author, btw.

@Anonymous manwha reader Me! I wanna know it. Any spoiler is fine

@Human Me too. He reminds me of [Oldest Dream], to be exact— so powerful yet so powerless. Actually, this arc reminds me of ORV, with its "constellation" "reader" "character" and all... 

@Galaxy I'm betting it's his senpai. The eye glasses guy who's obsessed with him

@Yaun I'm also 18 yrs old. Bi/pansexual girl (sorry I don't quite sure bout my sexuality yet), sucker to pretty faces. Also love and addicted to bl mangas/mahuas/manhwas. I would like to be your friend, unfortunately I'm from Philippines

@Shirayuki thanks so much

@Shirayuki can u tell us what site is it

@Shawneelynn  thank you so much. Well there are two stories that I'm looking for; manga, and mahwa. 
The manga is bl. It was about two middle)/highschool boys. They hate each other (but not to that extend)they were like rivals/enemy. Then one day something hit the head of the mc (if I remember it correctly, it's water bottle) then he passed out. When he woke up, his 'rival' was acting strangely. Well actually he was in another universe. And his supposedly 'rival' was his 'lover' in that world. And while he's spending his time there, he was falling for the ml little by little. Then he woke up/goes back to his world (I think it was because something hit his head again), then meet his ml. Then after going back to his original world, he realized that his ml there was actually like him. (His ml in his of world was jealous to his other self of the other world) 
The mahaba was about idol. If you know the "debut or die" it was similar to that (going back in time, becoming a k-idol, something like that). The scene that really stays in my head is when they were thinking what to perform, the mc suggested a concept about "zombie". His teammate look shocks and amazed on his idea because it was unique. It made the mc confuse because it was actually common concept, then he realized that the concept of the zombie is common in his time, there are little to none that uses the zombie as a concept for performance. Also for what I remember, there is this character that kinda like bae sejin. He looks like he's jealous to the mc, but he actually likes/ idolize him. 

(I'm sorry about the wrong grammars, eng is only my second language. Also sorry cause there are lot of things that I'm not sure with)

@Jjk It's "Grieving You"/"For you who griees"