As a data point, I knew about Hadrian and Antinous' relationship, but can't remember where I learned it. I would say that I have an above-average knowledge about the Roman empire, but it's hardly my primary area of interest.

(Speaking of knowledge of historical gays, I was amazed at how many people around me (including queer people), had no idea who Sappho was! Maybe my baseline idea of "how much most people know about history" needs to be recalibrated...)