Hate to disappoint everyone but this comic is a romance melodrama where the crux is a system that uses genetics and stuff to pair strangers together. That means showing the upsides and downsides of the system, and since gay people exist, it's reasonable to also show a gay person's relation to the system.
Hate to disappoint everyone but Nisaka's sexuality has been implied since at least chapter 27, so this part has been long overdue.
Hate to disappoint everyone but developing Nisaka as a character doesn't turn this into “gay manga”.
Hate to disappoint everyone but if you think that showing that gay people exist means “pushing the lgbt agenda”, you are probably a shitty human.