When we root for a relationship (often referred to in internet culture as "shipping," derived from "relationship"), we are actually rooting for the characters to become their best selves. The resolution of the romantic arc is intrinsically tied to the resolution of the character arc.
Pacing is crucial in relationships.
Furthermore, romantic subplots often act as the primary vehicle for character growth. In a thriller, a character might grow by overcoming a physical obstacle. In a romance, a character grows by overcoming their own emotional defenses. The "wall" that stops the couple from getting together is almost always internal—fear of abandonment, past trauma, or pride. HDSex-Positive