It should be, I just bought it yesterday. Maybe check your search settings to make sure you can see adult games.
I cannot find it anymore. I know it was available some months (weeks?) ago. My settings are correct so i should be able to see/find it. I mean other adult games of the same "quality" are offered to me still.
Edit 1: Strangely the lust epidemic steam community page is still there though...
Edit 2: Ok, it says that it is not available in my country right now anymore. Until further notice.