I don't think they are implying she was faking it before, just that it went from 'wasn't as scary as they said', through: 'this is actually quite nice', to 'The little death'
This is genuinely a really nice manga. When romance mangas end on the confession, kiss, graduation, etc...
This is the stuff you'll miss. A couple being lovey dovey throughout their life together. Moving into a home together. Etc etc.