I made every last of my NPCs and the automatic marriage option is turned off on my Mccc so the married couples are married because I decided it and created them like that (if that makes sense). The girlfriends/boyfriends are the ones who are already married to other unrelated sims but the game chooses them to become the lovers of the roommates instead of single sims. It's pretty weird...
I tested in a new game without mods and the game generated a new NPC for a roommate but the girlfriend was generated before him and she was single but the thing is, before my sim asked the dude to be a roommate, they had started a romance together and he was already my sim's boyfriend. So even without mods, in a new save, the game makes the roommates not faithful.
I just woke up and didn't have my coffee yet so my English may not be in the best of shape here hahaha
