A Conspiracy of Love (1987)

One thing she could always count on was having her grandfather to talk to... until her parents decided to divorce.

A woman's husband apparently has deserted her and their daughter. So she decides to get on with her life which might include dissolving their union and seeing someone else. However, her in-laws, her husband's parents feel that she's acting very hastily, so she leaves their home with her daughter whom they love very much. She decides to limit their access to her daughter, but grandfather and granddaughter see each other on the sly.