As told sa pamamagitan ng Mark Shwann himself, Brooke Davis was meant to bring a lighter side to the show. Even from the first two episodes you began to see darkness in ALL the characters (Peyton with her art, Lucas and his dan situation, Nathan and his Dan situation, and Haley seemed mysterious, like there was something we didn't know). So, with all of this mystery and darkness in the show, they needed someone fun, hot, and typical. But, as the ipakita grew on you began to see under her appearance as miss superficial, bitchy, popular slut and begin to see something madami in her. We learn madami about her in season 1 episode 8, when she and Lucas start to having a connection.
So, her original purpose was to be a slut that wasn't most liked... but her susunod purpose was to be the character that grows. The one that becomes kind, heart-felt and have completely unexpected success in a talent other then sex. During her growth you understand that she is madami intelligent and loving then you saw in her first skin as a heartless slut.
As for her first serious relationship she chose Lucas, who brought out the best in her. Even if it didn't work out, Lucas is one of the main reasons she is so amazing today. There is no tanong that ofcourse she would still be a good person, but maybe we wouldn't see as much good qualities as we do now if it wasn't for Lucas being in B. Davis's life.

As for the pag-ibig triangle, the point to this, I beleive, was to ipakita viewers that B.Davis has a HEART. During the betrayel and deception and pain that was thrust upon her, she was breaking on the inside, not sure how to handle such strong emotions because she has never been in a serious relationship before. But, the great thing about the pag-ibig tatsulok was that she didn't go back to complete sluttiness, she slept with felix with her stupid "friends with benifits" gig, but even during mga kaibigan with benifits with such a jerk she couldn't stay away from serious relationships, sharing her puso with madami people. I think she learned a lot from Lucas and The Peyton/Lucas/ Brooke triangle.

Brooke is an amazing person and I respect her so much for her risk-taking, selfless, genuine personality.
B.P.D<3