science fiction for grown ups, which was -- and still is -- heterosexist, mostly about men and women falling in love:
A. E. Van Vogt, Two Hundred Million A.D. (1943): L Onee was waiting. Together they closed and sealed the door. Together, they went up out of the darkness into the light.
Raymond Jones, Man of Two Worlds (1951): "I want to marry you] more than anything else in the world,” Elta said. She drew close and laid her head against his shoulder.
Michael Moorcock, The Wrecks of Time (1966): She winked at him. He grinned and winked back. They walked into the house.
John Brunner, Interstellar Empire (1976): She came down the steps to Ordovic, and put her arm around his waist, smiling.
R. M. Meluch, Wind Dancers (1981): “ Shall we go to bed together, get drunk, or start a fight in a bar?" Roxanne hooked his arms. "One of those.‟”
So I began reading. And kept reading.
The Sands of Mars (1951), A Fall of Moondust (1961), Imperial Earth (1975): no heterosexual romance.
When Clarke revised the novel into The City and the Stars (1956), he gave Alvin a girlfriend in Diaspar, like the Hardy Boys have girlfriends in regular time, but she is completely forgotten once he begins the adventure.
Childhood's End (1953): Galactic overlords land on Earth and transform all of the children into a new, advanced species, another entry into the "threatening gay kid" genre.
Gary Lockwood in the movie) jetting out toward Jupiter in the Discovery One, until the computer Hal gets jealous.
Arthur C. Clarke was well known in the science fiction community as gay, although he never came out publicly (when asked by a reporter, he always gave a coy response like "Why? What have you heard?").
In 1956 he moved to Sri Lanka, which being gay was legal (Britain didn't decriminalize homosexuality until 1957). He stayed there until his death in 2008.