I think if Sakai had told Nishimura about his crush towards him, Nishimura would have put an effort and start to like him back. How would Nishimura know that Sakai have a crush on him if he didn't tell him. I respect Nishimura for letting Sakai to continue his relationship with Kitada even after they become lovers. He did not feel possesive or jealous of them and accepted that Kitada is a part of Sakai's life which makes him grateful of Kitada of being there for Sakai. Just like how Sakai didn't know about Kitada's feeling without him telling Sakai, Nishimura too wasn't aware of Sakai's feeling towards him and he sacrifices by letting Kitada and Sakai to continue their relationship for the sake of Sakai's happiness because he started to love him after knowing Sakai's feeling towards him which Sakai should have told him earlier.
I think if Sakai had told Nishimura about his crush towards him, Nishimura would have put an effort and start to like him back. How would Nishimura know that Sakai have a crush on him if he didn't tell him. I respect Nishimura for letting Sakai to continue his relationship with Kitada even after they become lovers. He did not feel possesive or jealous of them and accepted that Kitada is a part of Sakai's life which makes him grateful of Kitada of being there for Sakai. Just like how Sakai didn't know about Kitada's feeling without him telling Sakai, Nishimura too wasn't aware of Sakai's feeling towards him and he sacrifices by letting Kitada and Sakai to continue their relationship for the sake of Sakai's happiness because he started to love him after knowing Sakai's feeling towards him which Sakai should have told him earlier.