The author is doing a horrible job with Nishikata's characterization. He is basically the same nervous child despite being an adult who is already married with Takagi and had a daughter with her. I mean, how the fuck can you get flustered over an indirect kiss when you already had sex with her? How is that even fucking possible?
By this point, I'm starting to think she was artificially inseminated or something because I can't picture these two having any skinship whatsoever.