Samaritan Girl(2004)

Let him that is without sin first cast the stone at her

Jae-Young is an amateur prostitute who sleeps with men while her best friend Yeo-Jin "manages" her, fixing dates, taking care of the money, and making sure the coast is clear. When Jae-Young falls in love with one of those men, she suppresses her feelings towards him in respect of her friend who's jealous.