She's very used to people kissing up to her to gain favor with her in hopes of getting something out of it so he's actually a breath of fresh air. He doesn't want anything, doesn't need anything, he just lets her hang around him and eventually they got close.
Slowly, and yet suddenly, they fell in love and didn't notice until he sat at her kitchen table getting a cut on his cheek cleaned up and getting scolded for his stupid reckless fight.
“They were talking shit about you! Was I supposed to let them?!”
“People have said worse about me, why let some stupid remark about me get to you like that?!”
“Maybe because I love you, you dumbass!”
“Don't call me a dumbass you jerk! I love you too!”