BISEXUAL HE IS BISEXUAL. Why does the bisexuality not exist for authors?

It is true that manga and manhwa authors want to ignore it exists, but like many people mentioned: Jaehyuk is too dumb to know that's a thing

Or maybe smthng like now that he is with garam he doesn't even find girls attractive or smthng

But that's normal for non poly people who just started a relationship, like, not finding anyone else attractive. Then after a while you might, but you still prefer your partner over anyone else. You don't list lose your bisexuality