Mystery song in the movie 'good posture ' which isn't in the soundtrack.

In the film 'good posture '. At 30 minutes into the film, Lilian leaves a note for Julia, then leaves the apartment and a song begins with piano. It plays briefly until she arrives at her ex boyfriend Nates house. They talk, then as she leaves the song continues again until she arrives at the dog park where she speaks with Julia's dog walker. This song isn't in the credits, or the soundtrack. And no music matching app can find it for me. Please help, it's driving me crazy.