There are several good authors who set their tales in Thailand. My favorite is John Burdett, who started a series with Bangkok 8. It was really good.
Not that any of these are gay, but I also like Christopher G. Moore and his Vinnie Calvino detective stories.
Another favorite is Timothy Hallinan, who writes the Poke Rafferty series about a guy who successfully marries a bar girl.
Currently I am reading a novel called Kingdom of Make-Believe. I am only a quarter of the way through, and again it is a straight story, but the author's descriptions of Thailand are superb. He alternates the present with a time 20 years ago when he lived there. Nostalgia City for me. A lot of it is set in the old capitol of, and now famous ruins, Ayutthaya.
Dean Barrett is the author.
I thought I had the name of another author on the tip of my tongue, but sadly, memory fails. Maybe I will recognize it when you post the names of your favorite authors writing about Thailand.