Idk I just feel like it's different from what Guren feels for other squad members. Especially because how he literally ended the world for him and the squad. Also *light novel spoiler* the moment when his squad was revived, Shinya wasn't. And Guren was so devastated. From my point of view, this section sounded like he ended the world for (mainly) Shinya:
"For that, just for a moment’s pleasure and attachment, Guren sold the world.
So,
“……..Shinya, he needs to be revived here.”
He said.
If he couldn’t, then there was no point in touching the taboo."
So this brings me to the question: what exactly is Shinya to Guren?