Characters in a sweet romance should be focused on getting to know the other person and building a lasting relationship. By their actions and dialog, the story should move along and let the characters get to know each other on a personal level. As your characters become closer, show their affection for each other by the way they react to one another and how they treat each other. This can be as simple as an affectionate word or touch.
Motivation and conflict move the plot forward by giving one or both of the main characters a reason to reach their goal. The motivation could be the prospective romance or something in one of the character's personal lives that causes them to seek out the other. As the plot moves forward, the characters should learn about each other and be drawn together. A hug, hand holding or chaste kiss is acceptable as they handle the conflict together. Add romantic tension by placing them in situations where they must depend on each other for something. Does the hero need something from the heroine? Does the hero rescue her from a difficult situation? Put the characters together where they can share personal feelings and get to know each other. As the characters are focused on each other and their mutual goal, let the romantic relationship develop.
Declarations of love or caring heighten the romantic tension. Your characters can remain chaste, or if they're headed for the bedroom, you can infer what is happening without actually showing the love scene. This can be done by letting the couple head up the stairs or into the bedroom and shutting the door. Your next scene would begin hours later, after the inference of the love scene.