Georgy Girl (1966) on Netflix

Twenty-two year old Georgina Parkin - Georgy to her friends - is a Plain Jane of a woman who beats to her own drummer. She grew up in the household of wealthy James Leamington, Georgy's parents being the household domestics. Middle aged Leamington, who had provided for Georgy's every need while she was growing up, offers Georgy a business proposition, all written in a formal contract: he will provide for her whatever she wants if she becomes his mistress. She never really directly provides him with an answer. Meanwhile, Georgy shares a flat with Meredith Montgomery, a beautiful but self absorbed woman. Partying all the time without him, Meredith is dating Jos Jones, who hangs around with Georgy while Meredith is out partying. Jos and Georgy have a good time together, Georgy who secretly loves her flatmate's boyfriend. Solely out of boredom, Meredith, who is pregnant with Jos' child, proposes she keep this one (she's previously had two abortions without much thought on the matter) and that she and Jos get married. The plan is for Jos to move into the flat, Georgy who is free to do as she pleases. As Meredith's pregnancy progresses and after the baby arrives, the life of Georgy, Jos and Leamington adjust to accommodate the change. By choice, Meredith's life is the one that doesn't.