Hey @SanWrites37, I'm glad you reached out to ask this question. I wrote Bella as a complex character in Winter's growth journey. She was toxic to some extent and did have feelings for David.
I left it open for readers to guess her ending but if we follow my version of her story then, after Winter was drugged she stopped being friends with Bella. This shows her growth as a character learning to build boundaries.
So yeah, she was an important side character.
She didn't end up with David cause he never really liked her back (If you remember he had feelings for Jade since long back. It's mentioned in one of the near-ending chapters).
I believe we've all had a complex friend like this at some stage of our life, so that's about it