Story search - gay, aliens with 3 sex-phases

[sunandshadow]

I don't know whether I read this story on Lit or not, but I also don't know of another forum where people would be likely able to identify it. The story involved aliens who empathically got pleasure from humans having sex nearby. The aliens only abducted male humans, I think one of the justifications given for this was that males radiated sexual pleasure more strongly. The aliens themselves had two vagina-like slits in their stomachs that led to a shared uterus, and they also had a penis-like organ noticeably bigger than the average human penis. The aliens went through three sexual phases in a pattern like this: male type A -> female, male type B -> female -> male type A, etc. I think each phase lasted about a month. The aliens also had some tentacle things with hooks that administered some kind of drug. This was a novel-length story.

So, if anyone remembers a title or has a link for me, thanks in advance!