PSA: ULMF search is now back online
I know this,played this, but failed to find it again.
To add to the above: there was a simple top-down map of the mansion; you used it to move from room to room. The key point of the story happened in the backdoor mansion (like a big shed/mausoleum in the garden behind the mansion proper. It was covered in vines.).
You chose one heroine among the 3 at the start - they split up at the beginning, because that's the obvious thing to do(?!), but you met them now and then to advance the story.
Every heroine had a different route through the mansion, and very different storylines. There were many possible endings.
I don't remember the H at all (so it was probably guro) but they were static CGs. Probably 800x600, Nocturnal Illusions-style.