The answer to both is simple.
They're Korean, and in Korea and Most of Asia it's considered taboo to be Gay or Lesbian and brings dishonor on your family and yourself because you can't propagate children to give to society, and since their all more communal, it means that there will be less people to join workforce, less ways to make s name for you family, which means more shame, as more people makes the community stronger, which makes the country also stronger.
It's not a concept alot of the rest of the world has, so it's difficult for most people to grasp unless you've been exposed to it for an extended period of time.
As for the Rumour Mill stuff. It is very common in Asia to have s very Harsh rumour mill flying around during high school, as the tact that they are supposed to have when older(as most of their societies are based around a keepyour thoughts to yourself unless you need to speak out something model, along with a 'insult others while maintaining the high geound/gracefully insulting others' type way to Express ones opinions, which develops as they are more cemented into society after high school and usually solidifies around college or temp work, and usually why 'yankee/ganster/punk' behaviour is commonly shown in series to be from mostly drop outs of either college or high school types) is not there as of yet, so instead of doing so in hushed corners, it tends to be done more in a shaming mannerism such as would happen at family gatherings as they all think of themselves as a community in the schools, meaning closer relations to what a family is seen as, or a group of extremely close friends.
I'm not sure if I stated as much as you needed for these explanations to make full sense, however it is late and I need to sleep, so please excuse me for now.
"Why do people care so much about if a guy is gay or not?.....it's 2018 and the teenagers are heavily influence by western media and opinions so why do they make a big deal about such a thing?" Its 2018...and yet why do i see gay kids killing themselves cuz they got bullied? Just cuz lots of people nowadays "agree" tht your gender or whtever doesnt matter in a relationship doesnt mean everyone in the entire world agrees w it. Teenagers are influenced by western media sure...but how about adults? Most adults are still stuck in the traditional way of thinking tht a dude can only end up and marry a girl. Why do people care so much about if a guy is gay? Uhh...duh it's cuz lots of people still think tht liking someone the same sex as u is "abnormal". So wht if people talking about the rumor aren't close w them? They'll still care. Why? Cuz they're afraid tht it'll spread and their parents and relatives fill find out. They're scared they're gonna get judged.
So mangas are making a big deal out of it cuz obv it's still fucking happening.
"I can say for a fact when there was crap going around about my friend being bi that I never once thought 'What if she likes me? How disgusting' and ignored her. If anything, I felt more hurt about the fact that she didn't share it with me and instead with someone who wasn't as close" just a question....did u ever realize how shitty your friend mustve felt when the rumor got out??? I get why you're concerned about why she didnt tell u first...u wnna be there for her and say shit like "dont listen to them"....it comforts them sure...but it's not everytime tht it works...maybe first figure out why she didnt tell u. Soemtimes...people focus more on wht others thinks thtn wht their friend thinks.
As for the gossip shit....again...mangas are just emphasizing how scary it is for someone to know about your deepest secret. Wht if people find out my deepest secret? They'll syrely think differently of me...thts wht they're focus on cuz thts wht theyre scared of. And again...like the other person said...people in asia are terrible at gossiping. They will judge u in anyways they can. Ik cuz thts wht i experience when i was in my home country and thts still wht i hear and see now.
Sry if the first part seems harsh......You're a good person for thinking tht people shouldtn care about wht other's sexual orientation is..but maybe try and see how it rly is in real life and whts spreading around online. Not everyone has the mindset of "oh idk them so idc". Also...western media aint tht acceptable about gay people either...
For the last few years, a few things about yaoi school mangas and school mangas in general have confused me to no ends and I'd love if someone had a proper answer to them and could please share this knowledge that seems to go over my head.
1. Why do people care so much about if a guy is gay or not? Especially if it's just rumours and the persons not really your close friend?
I mean perhaps it's because Japan is a conservative place and all but it's 2018 and the teenagers are heavily influence by western media and opinions so why do they make a big deal about such a thing? Coming from a girl who (admittedly) partakes in quite a lot of gossip and has attended both public and an all-girls school (which is where gossip becomes 100x worse) and has had similar situations happen around me, I can't understand at all why. It's not like these people are particularly close to the people involved (I mean best friend sort of way) so it's not like they are feeling betrayed or anything. I can say for a fact when there was crap going around about my friend being bi that I never once thought 'What if she likes me? How disgusting' and ignored her. If anything, I felt more hurt about the fact that she didn't share it with me and instead with someone who wasn't as close (though I do understand her reasoning).
And No 2. Why are high school kids in manga always so horrible at gossiping?
As I said before, I do enjoy a bit of juicy gossip and drama and I can assure you that anyone (especially girls) are a tad more discreet in these sorts of sensitive situations. Most people won't talk about such things so blatantly and would keep it more to lunch time/time when said person is not there. I can understand a bit more why guys aren't the best at keeping their opinions to themselves (because I'd say their experience is quite different than your average teenage girl, especially those in higher grades) but even the girls? Do the Japanese not know how to gossip? I'm not saying not knowing how to gossip is bad (Honestly, it's probably better not to know) but it's just a bit more believable if they draw/write it properly. I get it's probably for dramatic effect but it does irk me quite a bit.
So if anyone knows the true reasons to my questions, please do answer me and thanks for spreading your knowledge^^