It was as though something large and scaly erupted into life in Harry’s stomach, clawing at his insides: hot blood seemed to flood his brain, so that all though was extinguished, replaced by a savage urge to jinx Dean into a jelly.
"This was a deserted corridor ‘till you came butting in!" said Ginny. Dean was looking embarrassed. He gave Harry a shifty grin that Harry did not return, as the newborn monster inside him was roaring for Dean’s instant dismissal from the team.
Harry… felt disoriented, dizzy; being struck by a lightning bolt must be something like this. It’s just because she’s Ron’s sister, he told himself. You just didn’t like seeing her kissing Dean because she’s Ron’s sister… But unbidden into his mind came an image of that same deserted corridor with himself kissing Ginny instead… the monster in his chest purred… but then he saw Ron ripping open the tapestry curtain and drawing his wand on Harry, shouting things like “betrayal of trust”… “supposed to be my friend”…
J.K. Rowling, Harry Potter and the Half-Blood Prince, pg. 286-287, 289