I'm pretty certain from having watched whole neighbourhoods for a while precisely for this that the relationships that start out at a half-full bar when you see them are not created because Sims met each other in the background of your gameplay but rather by a separate game mechanic entirely.
There are two mod options for deleting them:
MC Command Center (you only need the base module, I believe)
UI Cheats Extension
Haven't found anything out there that prevents them, but I'd be your biggest fan if you can, as a rotational player who wants to have full control.
