Pennies from Heaven (1978)

Arthur, a sheet music salesman, has an ear for the hit tunes, but nobody will trust it. And his imagination often bursts into full song, building musical numbers around the greatest frustrations in his life. He meets an innocent young school teacher, Eileen, who seems to hear the same music, but when Eileen learns that he's married, and that she's pregnant with his child, she runs away. Arthur gives up everything to find and protect her, but fate and the music haven't finished with Arthur Parker.