The Purple Ring (1968).
I’ve not read any of Carl Corley’s novels but their covers become familiar once you start searching through archives or articles devoted to the gay pulps of the 1960s. Corley was unusual in this field in authoring his books under his own name (most gay and lesbian pulps are credited to unlikely pseudonyms) as well as providing the cover art for each title. His paintings try for more of a distinctive look than the usual standard of the time— generally two half-dressed guys pouting at each other—but then he was illustrating his own work so could tailor the art for the story. This kind of fiction is a lot more visible now than it used to be, attracting the attention of queer historians and academics, but there’s still no dedicated site for many of these artists and writers beyond Gay on the Range. There’s a couple more Corley covers on Flickr (here and here) but for now The Haunted Lamp seems to have the best collection.