The main narrative follows youngsters Al and Olive and their respective journeys towards saying those three words for the first time. However, the story is interspersed with inputs from different couples in evidently very different relationships.
| Actor | Role |
|---|---|
 Georgia TennantOlive | Olive |
 Joel FryAl | Al |
 David TennantMark | Mark |
 Nina SosanyaLily | Lily |
 Ann QueensberryMary | Mary |
 Christian BrassingtonHarry | Harry |
 Ingrid OliverCammy | Cammy |
| MMatthew WilsonMatt | Matt |
| HHelen CarterHelen | Helen |
 Adam Paul HarveyLuke | Luke |
 Olivia LeeFrankie | Frankie |