Grace is back from her brief absence from the show, and she's having marital issues. She doesn't know how to fix them, so she is not returning to Cambodia to be with Leo. They are going to wait until Leo gets back and see where they are.
Karen: 60s London school, Sidney Poitier, Lulu.
Karen's references to school in 60s London and her black teacher, as well as her phone call at the end of the show, are taken from To Sir, With Love, a 1967 film set in an East End school, starring Sidney Poitier and Lulu.
Episode Title: Swimming From Cambodia.
This is a reference to the 1987 movie "Swimming to Cambodia."