This book is by Roni Denholtz.
Brett Ryerson believes his first love, Julie Merritt, is engaged to Warren Wesley. He decides to borrow her for a few days to convince her that Warren is wrong for her. What he does not know if that she had broken her engagement but promised not to tell anyone until after the celebration for Warren's win as mayor. Brett introduces her to several people who have much to tell her about Warren.
Julie decided to go along with him to see if she still had feelings for him and if he had any feelings for her. His parents are able to see that she does before he realizes that he does. He learns from someone else that she had broken the engagement and wondered why she had not told him. She was about to say something just before he learned her secret.
I have not met Roni but we are both fans of Judy Bolton and I have read other books she has written. I have loved all of them and would recommend them to others who like romance.