Even the voyeur friend of MC tells him to give up on the slut (who for some reason wants to have MC at her arm's reach) despite she is hooked on sex with the bully as he witnessed together.
She's just being practical, gotta hold on to her future provider. Enjoy sex with the bully while waiting for MC to graduate from school and when he gets a stable job, monkey branch to him while also still fucking the bully behind MC's back.