It is two completely different games.
The first one, it was her sister living with them. In the second one she was the MC's best friend.
The first one they had a foursome and the MC could choose to take the sister's virginity or allow the other man to do it
The first one the MC's girlfriend had a "free pass" during the fun, but then she left in the middle of the night and chose to cheat and have unprotected sex and be creampied. She and the new lover even hinted at continuing in secret. She came back to bed with the MC and speaking to her sleeping boyfriend said something about the fact that if he only new what they started. Then it ended.
Now the second one has nothing todo with the first. It is completely different. I was hoping to explore the first...
But oh well...
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 not. 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).