Rich Podolsky's book Don Kirshner: The Man with the Golden Ear
tells the story of how Darin introduced this song to Don Kirshner and Al Nevins, producers of the then-newly-formed Aldon Music. Kirshner and Darin were lifelong friends, having teamed up in their teen years before either one of them got their first break, having been best man at each other's weddings, and after Darin's tragically early death, Kirshner named his daughter Daryn after him. So when Darin made it big before Kirshner got established, he promised that he wouldn't leave Kirshner behind.
So a few weeks after Darin's new contract at Atlantic Records forced him to let Kirshner go as his manager, he dropped by Aldon Music to give them a preview of "Dream Lover," along with "Queen of the Hop." Kirshner relates that Darin sang it "as if he were performing it at the Copacabana nightclub." Afterwards he couldn't wait to tell Al Nevins about it.