Naoto's reaction to being told Satsuki might be pregnant says a lot. Yeah, they definitely did it that night, else he'd have a much more severe expression and he'll be saying "but we've never done it!" and then have some dramatic doubts about breaking up. The look of mild confusion is probably because they used protection, but nevertheless he rushed back because in any case, she's sick and needs someone to watch over her. Naoto here doesn't look like he believes she's pregnant, so I'll be disappointed next chapter if he actually got fooled and this misunderstanding persists.
Tokui having a gf came out of left field for me, so her name is Aki and she's a kuro gal. Seems recent enough for them to still be going out but I can't tell if that uniform is from their school.