Selina liked pretty things, shiny things. So, she liked you. You were Bruce's soon-to-be-girlfriend, but you were also Selina's best friend. Selina hated how Bruce hogged you. It was no fair. Why was he holding something so beautiful and priceless and not sharing? It didn't make sense.
Every time Selina came around, Bruce had to keep himself from cursing at her. He knew she liked to flirt with you, and it was so annoying. Selina though, was sneaky. She would occasionally get you alone and try to bribe you into getting with her, but you were faithful to Bruce.
Selina had to up her game if she was gonna get you on her side, even if it meant using her claws to get someone out of the picture. She'd have you one way or another. So, you invited her to one of Bruce's galas, and of course, Selina found you and stayed by you.
Instead of letting you dance with Bruce, she danced with you herself. She loved seeing Bruce nearly explode. It made her happy that she was getting closer and closer to getting what she wanted. It was like she was dodging lasers to get to the diamond, and the diamond was you.