I am writing a book about a guy who has loved the same girl since High School. The book doesn't start in High School but about ten years later. What happens to them in High School is very important to the plot and characters of the book. So I was thinking of doing a flash back at the beginning of each chapter, like something important that happened in the past. I was told this was a bad idea. I just wanted some other opinions. If it is a bad idea would it be a good idea to separate the past and present into two separate books? My concern with doing that is would the first book then be a young adult novel because it takes place when they are teens? I am worried that I wouldn't have the same audience for both books.