When did Rey and Neville officially get together (First date, kiss etc.)?
Neville realized he was in love during the Yule Ball. Rey, just a little before. But there was no confession until next summer (they were both shy and nervous about this! Mostly the thought of ruining a friendship in case the feeling was one sided). So during year 5 (order of the phoenix) they are together, just very discrete. They didn’t feel like letting everyone know (though some guessed, like Ginny and Hermione). They would only share little kisses when no one was around. During year 7, it was even more important for them not to let anyone know they were a couple, they didn’t want the Carrows to use it against them. They shared their first kiss without caring about being seen after the war.