I find that char in their brief is more hotter than being naked

I think he did, but remember; mungmung is very young back when he confessed, and his hyung was already an adult.
In Korea, being pdfile or even just being in a relationship with someone considerably younger than you is enough to ruin your reputation/life for good.
ML probably already had feelings for MC but rejected MC’s confession thinking that it must be just the MC’s confusion his closeness to ML with love.

Just my hunch.

U probably meant to reply to the comment below lol