“Learn to let go sometimes.” both Hee Do and Yi Jin grew up, their relationship failed to grow. They expected it to stay the same when they weren't the same people anymore. Yi Jin understood this fact more than Hee Do, but miscommunication, misunderstanding, and impatience took the best of their relationship. This drama was really enjoyable and i loved it. However, in context of the story, and as substantiated by the Hwa&Dam production company, the first love of Heedo and YiJin was each other. YiJin corroborates it in the final minute of the drama: Who is your first love? Na Hee Do.