I think it should be clear by now that Sekine has some form of Asperger's or Autism. He has emotions, he just doesn't understand and experience them the same way a neurotypical person would. Same with interpersonal relationships. All the people around him attributing motivations to him and yet they never believe him at face value when he plainly says, "i dont see the point/relevance" or "I'm not interested/don't care". I can definitely sympathize with that.