This song seems to be KP reflecting on memories of her ex. As she looks back on joyful memories such as them dancing in the back of cabs together she is also aware that at that point they were avoiding the issues in their relationship at that point.
It seems that this song is about her relationship with actress Amandla Stenberg as there are videos of them ‘Dancin’ in the back of a cab' together. Additionally, it would make sense as Stenberg is her most recent ex