I got one of those msg too! It say "three's a crowd for romance, and something something (don't remember, but I think it's different than yours". I click no, since I didn't know what it was about. But I think one of the female sim that my sim made friends with has a crush on her...haha
I got that once.
i had a small gathering at my apt. me and 2 male friends and i went to do the elevator woohoo. That pop up came up and i clicked yes. and the 3rd left the group so my sim and her romantic interest could go woohoo.
I got that too...but there wasnt anything romantic going on.
I had three sims in the house, One a couple and the other a maid.
While the wife was making potions, the husband asked the maid to help him practice making drinks. That was it...
And i got that pop up.
Yeah i get that. I have a sim couple who are happily and faithful and when my male sim decided to go to a job opportunity that came up. It comes up now and then and for no purpose cause none of them are even cheating.
Im getting that msg and my household only contains two sims, and they are sisters. I've got one in the basement sculpting and the other upstairs mixing skill gain drinks. I've checked and there are no other sims on the lot so im not sure what the msg means.