This is not a version of events Neville would have thought about. Ever. Because he thought he knew her all too well, in and out. In his mind, she was supposed to become angry with him and tell him to do something and he'd be able to watch from a close distance and get her to forget about the kiss and his confession soon enough.
This was not supposed to happen.
She was not supposed to become Scamander's bride.
She was not supposed to go.