The entertainment industry has a rich history of double acts. Pairs of people combining their talents in a single identity. Well... here's what they would look like as pairs of talented people combined into a single entity... I imagine.
Mark enters a relationship with Sophie (Olivia Colman) and finds, quite rapidly, that... he doesn't really like her. This isn't anyone's fault, neither are presented as terrible human beings. They're just fundamentally incompatible and only end up steamrolling into marriage due to crippling mutual loneliness.