Idea: My Other Lover
Ford Tillinghast thought the illustrations and diagrams in the old battered book he found in Grandpa’s attic were edgy and cool. So cool that he got a couple tattooed.
Then the weird visions started. He could see Them, the Others, ignored and trapped within a ghostly overlay of our world. Hungry, lonely, and indescribable. All too quickly he discovered they were also horny… and he’d just etched sigils from a copy of The Laws of Ruin all over his body.
Permanently.
***
Invisible sex with alien entities anywhere and everywhere all of the time? Check.
Idea is a combo of reading Lovecraft’s “From Beyond” and a short description of Las Regias de Ruina included in Nate Pedersen’s “The Starry Wisdom Library” (which is a great book for Lovecraftian bibliophiles and book arts folk).