I know pride months almost over (crazy), but here's some of my favourite queer composers!
Pyotr Tchaikovsky (1840-1893): Probably the most notoriously gay. Wrote some of the biggest and most famous ballets of the Romantic Period including Swan Lake and The Nutcracker. Also wrote a number of well-documented love letters to his numerous male lovers (ooooh). Also was in an ill-fated lavender marriage to opera singer Antonina Miliukova.
Benjamin Britten (1913-1976): Was an English composer and conductor, including the writer of several famous operas and orchestral works like A Young Person's Guide to the Orchestra and Peter Grimes. He was life partners with fellow musician Peter Pears for almost 40 years. Pears was a consistent muse for Britten and the inspiration for a number of his works. The 2 were buried together after Pears death in 1986.
Ethel Smyth (1858-1944): A passionate suffragette and composer (and Bi icon), Smyth wrote a number of works such as The Wreckers and The March of the Women. While she didn't receive as much fame as her male colleagues, Smyth is still considered an incredibly influencial and important modernist composer and was the first female composer granted damehood. Smyth held several passionate relationships and affairs with men and women alike, including fellow feminist Emmeline Pankhurst, philosopher Henry Brewster, Pianist Violet Gordon-Woodhouse and even Oscar Wilde's brother Willie.