A common pitfall in romantic writing is "The Prize" syndrome, where one character (usually the female lead) exists solely to be won by the protagonist.
They love each other, but they want different lives (e.g., one wants to travel, the other wants roots).
To avoid this, ensure both characters have their own goals, hobbies, and lives outside of the relationship. A storyline is much more dynamic when two complete people choose to be together, rather than two halves desperately trying to fill a hole. 6. The Power of the "Quiet Save"