I'd probably stop at 2-3 confessions. More than that, and the words begin to cheapen and sound insincere. Which is probably why the guy only blushed when he finally saw her serious confession. Not that the previous ones that she gave were any less.
She was probably confessing her feelings to him every time they met. In the hallways on their way to class? Time to confess! I'm the cafeteria eating lunch? Confession time!