Jazz Tangcay Artisans Editor Billy Eichner didn’t just write, produce and star in “Bros” — he also sings in it. The rom-com, in theaters now, follows the courtship between Bobby (Eichner) and the hunky lawyer Aaron (Luke Macfarlane), who meet at a launch party for a new dating app called Zellweger. Yes, named after the actress. Award-winning composer Marc Shaiman was brought on board to thread together the film’s score as the two characters stumble towards love, and out of love, and into love again. Shaiman credits Eichner with the song idea for the big ballad of “Love Is Not Love.”