It's true. Freaking out about a guy dumping you is self-fulfilling prophecy. Your jealousy and insecurity can cause him to feel that he needs some breathing room or to wonder what he's doing with you, and then your worst fear will come true. Best to play it cool.
Play it cool? I don't see anything wrong with this girl telling her boyfriend how she feels. Isn't communication the best way to create a strong relationship?