The male and female protagonists were childhood sweethearts. Later, the female protagonist went abroad and returned to China at the age of 18. How should the male and female protagonists interact and develop? This is a very interesting plot. Here are some possible steps: 1. The female protagonist returns to the country: The female protagonist should seize the opportunity to get close to the male protagonist and let him know that she is back. The male protagonist may be curious and excited and start looking for signs of the female protagonist to see if she has any impression of him. 2. The male protagonist takes the initiative: The male protagonist may take the initiative to chat with the female protagonist or invite her to participate in some activities such as watching a movie or eating. The male protagonist should show his enthusiasm and sincerity to let the female protagonist feel that he was interested in her. 3. Establishing a connection: The female protagonist can try to establish contact with the male protagonist through social media or text messages. The female protagonist should show her concern and friendliness to let the male protagonist feel her attention and interest in him. 4. Date: If the male protagonist is interested, the female protagonist can try to arrange a date. This date could be a walk in the park or a meal in a restaurant. The important thing was to let the male lead feel her sincerity and enthusiasm, as well as her interest in him. 5. Further development: If the male protagonist is also interested in them, they can consider further development. This may take some time and space, but both parties should communicate honestly and respect each other's feelings and decisions. It was important to note that when writing a novel, one needed to carefully consider the development of the plot and the behavior of the characters. The actions of the female protagonist and the male protagonist should be legal and respectful of each other's wishes and feelings. At the same time, the development of the plot should have a certain degree of logic and rationality to convince the readers.