You're correct that it's two completely separate games, but in your descriptions you have them reversed.
What you call the "first one" is the second version -- the one that is being actively developed.
The original game is the one with the MC's best friend (Jenni), the mother-in-law, and the succubus/demon. That game is a bit of a mess, but it's "complete".
The current game does have two separate and distinct paths that play out independent from each other, depending on whether you enable NTR or now. The initial release of that game only had the NTR path -- the foursome with the cheating scene you describe. The latest update of the current game (a couple of months ago) only included content on the Love/Vanilla path (relationship with Zoey).