I'm currently playing as a family of one Sim and a cat. The Sim got romantically involved with another, and I wanted to try and ask the other Sim to move in with the household. The problem is, from what I can gather this is a Friendly related option when talking. But this option does not appear for me in the talk options. I have seen it once when I was building the relationship between the Sims, but now I cannot find it anymore.
The Friendly talk options contain all sorts of stuff for me. My Sim has a lot of extra options in the Friendly screen (she's a Witch with various traits that give quite a few extra talk options in this screen). Note that their relationship is at the highest level: the bar is fully green.
So is it possible to ask that Sim to join the household, preferably without breaking up? Or is at this point marriage the only way to do this?