Deadly Temptation: My Athlete Brother Is Such a Flirt

Her legs had turned to jelly from all his flirting.

The heroine is about to confess her feelings to the boy of her dreams. All she wants is a sweet romance, but her best friend finds out first. Since she likes him too, she gets an athlete to flirt with the heroine.

The athlete wastes no time acting like they're already close, coming right out with his feelings and leaving the heroine completely flustered.