Stan Drake's The Heart of Juliet Jones #1

Julie tries to convince Eve that she must study to pass her math exam or she won't graduate from high school. But Eve rebels again her sister's nagging and vows to get even. When Julie arranges a study session with the math teacher who happens to be Julie's fiancé, Eve intentionally seduces him to get revenge against her sister. Gig finally comes to his senses when he realizes Eve was just playing him along, but it comes too late to save his relationship with Julie and he leaves town.