Creator Darren Star has commented on the character's progression. In his DVD commentary of the episode "Spring Dance", Darren notes Kelly's first attempt to romance Brandon Walsh in which she'd embraced her role as Spring Princess and used a largely forward and aggressive approach. He goes on to state that in the fourth season, when Kelly was prone to expressing her affections in a more gentle and compassionate manner. She made a greater impression on Brandon. This development is standardized one additional year later, via her aforementioned second pursuit of Brandon Walsh, which ends in success.
Time Goes On
Ultimately, throughout the first five seasons, Kelly gained an increasing degree of screen presence and growth. Amidst her continuing development, her role in launching the spin-off, her prominent triangle with Brenda and Dylan, her later affections with Brandon and the launch of a second triangle with Brandon and Dylan.
In season 5, she was faced with making a choice between the two, as a result of Brandon proposing and Dylan McKay confessing his feelings for her and asking her to leave with him on a trip around the world. She ultimately refused to make a decision. In the seventh season, however, she finally stated that she had chosen Brandon with the two remaining together for the majority of Priestley's stay on the series.
Following an arc that had Kelly getting shot in a drive-by shooting, amnesia and the rekindling the more physical side of their relationship, Brandon then went on to cheat on Kelly with a guest writer at his newspaper (an uncharacteristic move for Brandon who was always one of the more faithful characters on the show - especially given his feelings for Kelly and his strong desire to protect her just a few episodes prior to this arc). After discovering what he has done, Kelly breaks it off with him and tries to go on dates with other men, with Brandon interfering and trying to make her see how much he loves her. When she finally gives him a second chance, the relationship is wrought with jealousy and issues with trust, culminating in Kelly yelling at him that she's always scared that any girl she sees him with will be "the next Emma". Brandon, unsure of how to respond to the claim, asks her to marry him casual dresses and a shocked Kelly accepts, hoping it will heal them. A wedding is planned and they get as far as the wedding day before they mutually decide to call it off, realizing it's not right for either of them. They make a last ditch effort to save (or say goodbye) to their relationship before acknowledging that it's over. Brandon agrees to a job on the other side of the country and before he leaves, Kelly meets a new lawyer named Matt Durning - causing Brandon some jealousy at what might develop between the two, but not enough to make him stay in Beverly Hills. He ultimately leaves town (Priestley was leaving the show) and Kelly eventually moves on with Matt but sweater dresses there are subtle mentions throughout the rest of the series that she still has feelings for Brandon.
The Relationship Begins