Naegi got his floaty hearts for miss Kirigiri. And for more innocent, never-ever-leading-to-anything-because-it's-mostly-idolizing, I'd say he's got a crush on miss Morrigan
Kobra's got his crushing on Kenzi, something sort like how Naegi feels towards Morrigan but with Jet, and he might be developing some crushings on Scanty too
Apolie got some actual crushing on Naltei. But he doesn't even admit to himself that it's a thing. And he mostly freaks Naltei out a little and annoys him