
Its not explained well in the Manwha but Zenhya was only ever attracted to women and only had secx with women. So these het secx scene right in front of the MC were kinda like a vessel to outlet his frustration to being attracted to him on top on harassing him (cuz Zenhya is one crazy mf) Hence why he progressevely started to involve MC in these secx scene

The fact that you can't even elaborate something in a more sensible way is already funny.
No. They didn't need this scene to actually show ML's interest in MC. This whole sexual tension thing could've been pulled off in a more less disgusting way. And it's not as if there weren't any other BL ML's who became straight as a circle only after meeting the MC. So, no matter however you try to make sense of that whole scenario you'll find it unnecessary. But seeing you defend something like that seems like you liked it a lot. Makes me doubt you even like BL.

I felt so disgusted by those scenes ewww and guess what ?my gay friend read this one and commented that threesome was so disgusting but this fandom trashed my gay friend like heterosex in yaoi is not a big deal. Bl was supposed to meant for gay's so what the fuck with this fandom when gay guys or fujoshis hate this scenes. They don't even respect gay people's opinions here.
I still have no idea why the train sex was necessary? Like how doed this help the plot?? WAS VERY IMPORTANT TO HAPPEN??? This whole fiasco just made me hate the ML more. This guy is just another Ilay.