If you're talking about the friend who was obsessed with the MC(B) then it definitely affected the story where plot is concerned
He had an unhealthy relationship with the MC(B) or at least towards him, one the MC(B) didn't even notice or played oblivious about. That lead to proper boundaries not being set and even if they were set, like I said, it was an unhealthy relationship causing the friend to ignore those boundaries and then the MC(B) would do nothing about that. Due to this being added, in the story not only did it help with both the MCs(A & B) relationship but it also helped the MC(B) actually set proper boundaries and draw the lime with his "friend".
Even though others are saying it was unnecessary...it really wasn't lol, it just added more to the plot.
Saying that is like saying the MC(A) didn't have to be an artist, it's unnecessary, he could've had any other occupation...or that the MC(B) didn't need to have a rich background, it was unnecessary, he could've just been "normal".
These things are just added to give more "flavour" to the plot lol
Sorry I tried explaining this the best way I could
its fun, cute, nice
dont underatand why the friend had to end up being in love with muyeong. its like a one off thing, nothing really happens because of it. i mean its like whatever, didnt effect the story at all. but why was it included in the first place? to develop muyeong and seonho's relationship? didnt really affect their relationship if that was the case.
envisioning junseok is over muyeong and is in a relationship and is happy :)