boy and girl

Someone please explain this phenomenon to me. Boy digs girl, boy watches girl from afar, boy comes on to girl, girl responds with positive feedback, boy and girl kiss, girl makes effort with boy who she otherwise would not have noticed, boy freaks out. Girl wonders why. Boy tells girl that he never thought girl would like boy back. Boy walks away from it. Girl is left wondering. Had boy never opened the can to begin with, girl would not feel so bad. Girl kicks herself for falling for the attention and not the boy, because then girl would not feel so bad and boy would not be so freaked out.