Everyone says Cosmo composes for Hollywood, but Cosmo really composes for Don.
He was never supposed to be the leading man, it just isn't his style, so he stays behind the camera, where nobody gives him a second look. He plays his music, and cracks jokes about everything and anything (especially Lina), and goes with Don to premieres where nobody knows his name.
And he writes confessions in his sheet music, taps out Morse code with his tap shoes, always the same message: I love you.
He plays his piano, lets his eyes rest on Don lighting up the stage, and well, it's not exactly what they imagined in sleepy whispers, curled together on narrow and creaky cots after vaudeville performances in nowhere towns, but they're happy, aren't they?
After all, Don still comes home to Cosmo at the end of the day, dances around the kitchen while Cosmo cooks, and sings in the bath while Cosmo works, and hot dog, this really is better than anything they could dream up. Don acts, and Cosmo talks to anyone who will listen about how someday he'll write his symphony, and that'll be the day, won't it?
He even endures the jibber jabber of the Hollywood elites at stuffy Hollywood parties, cracks the jokes that make people look at him funny, but hey, he has a motto: make 'em laugh.
Make 'em laugh, because laughing means they don't look too closely about how, no matter what gals are draping themselves over Don like slipcovers for a couch, Cosmo and Don always go home together.
Make 'em laugh, because if they laughing, they're not seeing how Cosmo looks at Hollywood's leading man (and the way said leading man looks back at Cosmo).
Make 'em laugh, because if they laugh in all the right places they might forget to ask about Cosmo's symphony.
Because really, Cosmo composes with his heart, the melody spilling from his soul onto paper by way of his fingers, and the melody is one he taps out on Don's chest while Don sleeps in his dressing room between takes.
And the melody is really Don's heartbeat because Cosmo's symphony is for Don, it always has been.
Composing for Hollywood is his day job, but his symphony sounds nothing like his usual work, because this isn't for Hollywood.
His symphony is gin and tonic kisses, and callused fingers, and the brave, brassy notes of a hero's song. It's for Don.
It always is.